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1 nigel 63 <html>
2     <head>
3     <title>pcreapi specification</title>
4     </head>
5     <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
6 nigel 75 <h1>pcreapi man page</h1>
7     <p>
8     Return to the <a href="index.html">PCRE index page</a>.
9     </p>
10 ph10 111 <p>
11 nigel 75 This page is part of the PCRE HTML documentation. It was generated automatically
12     from the original man page. If there is any nonsense in it, please consult the
13     man page, in case the conversion went wrong.
14 ph10 111 <br>
15 nigel 63 <ul>
16 ph10 691 <li><a name="TOC1" href="#SEC1">PCRE NATIVE API BASIC FUNCTIONS</a>
17     <li><a name="TOC2" href="#SEC2">PCRE NATIVE API AUXILIARY FUNCTIONS</a>
18     <li><a name="TOC3" href="#SEC3">PCRE NATIVE API INDIRECTED FUNCTIONS</a>
19     <li><a name="TOC4" href="#SEC4">PCRE API OVERVIEW</a>
20     <li><a name="TOC5" href="#SEC5">NEWLINES</a>
21     <li><a name="TOC6" href="#SEC6">MULTITHREADING</a>
22     <li><a name="TOC7" href="#SEC7">SAVING PRECOMPILED PATTERNS FOR LATER USE</a>
23     <li><a name="TOC8" href="#SEC8">CHECKING BUILD-TIME OPTIONS</a>
24     <li><a name="TOC9" href="#SEC9">COMPILING A PATTERN</a>
25     <li><a name="TOC10" href="#SEC10">COMPILATION ERROR CODES</a>
26     <li><a name="TOC11" href="#SEC11">STUDYING A PATTERN</a>
27     <li><a name="TOC12" href="#SEC12">LOCALE SUPPORT</a>
28     <li><a name="TOC13" href="#SEC13">INFORMATION ABOUT A PATTERN</a>
29     <li><a name="TOC14" href="#SEC14">OBSOLETE INFO FUNCTION</a>
30     <li><a name="TOC15" href="#SEC15">REFERENCE COUNTS</a>
31     <li><a name="TOC16" href="#SEC16">MATCHING A PATTERN: THE TRADITIONAL FUNCTION</a>
32     <li><a name="TOC17" href="#SEC17">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a>
33     <li><a name="TOC18" href="#SEC18">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a>
34     <li><a name="TOC19" href="#SEC19">DUPLICATE SUBPATTERN NAMES</a>
35     <li><a name="TOC20" href="#SEC20">FINDING ALL POSSIBLE MATCHES</a>
36     <li><a name="TOC21" href="#SEC21">MATCHING A PATTERN: THE ALTERNATIVE FUNCTION</a>
37     <li><a name="TOC22" href="#SEC22">SEE ALSO</a>
38     <li><a name="TOC23" href="#SEC23">AUTHOR</a>
39     <li><a name="TOC24" href="#SEC24">REVISION</a>
40 nigel 63 </ul>
41 ph10 691 <br><a name="SEC1" href="#TOC1">PCRE NATIVE API BASIC FUNCTIONS</a><br>
42 nigel 63 <P>
43     <b>#include &#60;pcre.h&#62;</b>
44     </P>
45     <P>
46     <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
47     <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
48     <b>const unsigned char *<i>tableptr</i>);</b>
49     </P>
50     <P>
51 nigel 77 <b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
52     <b>int *<i>errorcodeptr</i>,</b>
53     <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
54     <b>const unsigned char *<i>tableptr</i>);</b>
55     </P>
56     <P>
57 nigel 63 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i>,</b>
58     <b>const char **<i>errptr</i>);</b>
59     </P>
60     <P>
61 ph10 691 <b>void pcre_free_study(pcre_extra *<i>extra</i>);</b>
62     </P>
63     <P>
64 nigel 63 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
65     <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
66     <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
67     </P>
68 ph10 691 <br><a name="SEC2" href="#TOC1">PCRE NATIVE API AUXILIARY FUNCTIONS</a><br>
69 nigel 63 <P>
70 ph10 691 <b>pcre_jit_stack *pcre_jit_stack_alloc(int <i>startsize</i>, int <i>maxsize</i>);</b>
71     </P>
72     <P>
73     <b>void pcre_jit_stack_free(pcre_jit_stack *<i>stack</i>);</b>
74     </P>
75     <P>
76 ph10 692 <b>void pcre_assign_jit_stack(pcre_extra *<i>extra</i>,</b>
77 ph10 691 <b>pcre_jit_callback <i>callback</i>, void *<i>data</i>);</b>
78     </P>
79     <P>
80 nigel 77 <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
81     <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
82     <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
83     <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
84     </P>
85     <P>
86 nigel 63 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
87     <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
88     <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
89     <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
90     </P>
91     <P>
92     <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
93     <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
94     <b>int <i>buffersize</i>);</b>
95     </P>
96     <P>
97     <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
98     <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
99     <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
100     <b>const char **<i>stringptr</i>);</b>
101     </P>
102     <P>
103     <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
104     <b>const char *<i>name</i>);</b>
105     </P>
106     <P>
107 nigel 91 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
108     <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
109     </P>
110     <P>
111 nigel 63 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
112     <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
113     <b>const char **<i>stringptr</i>);</b>
114     </P>
115     <P>
116     <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
117     <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
118     </P>
119     <P>
120     <b>void pcre_free_substring(const char *<i>stringptr</i>);</b>
121     </P>
122     <P>
123     <b>void pcre_free_substring_list(const char **<i>stringptr</i>);</b>
124     </P>
125     <P>
126     <b>const unsigned char *pcre_maketables(void);</b>
127     </P>
128     <P>
129     <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
130     <b>int <i>what</i>, void *<i>where</i>);</b>
131     </P>
132     <P>
133     <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
134     <b>*<i>firstcharptr</i>);</b>
135     </P>
136     <P>
137 nigel 77 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
138     </P>
139     <P>
140 nigel 63 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
141     </P>
142     <P>
143     <b>char *pcre_version(void);</b>
144     </P>
145 ph10 691 <br><a name="SEC3" href="#TOC1">PCRE NATIVE API INDIRECTED FUNCTIONS</a><br>
146 nigel 63 <P>
147     <b>void *(*pcre_malloc)(size_t);</b>
148     </P>
149     <P>
150     <b>void (*pcre_free)(void *);</b>
151     </P>
152     <P>
153 nigel 73 <b>void *(*pcre_stack_malloc)(size_t);</b>
154     </P>
155     <P>
156     <b>void (*pcre_stack_free)(void *);</b>
157     </P>
158     <P>
159 nigel 63 <b>int (*pcre_callout)(pcre_callout_block *);</b>
160     </P>
161 ph10 691 <br><a name="SEC4" href="#TOC1">PCRE API OVERVIEW</a><br>
162 nigel 63 <P>
163 nigel 93 PCRE has its own native API, which is described in this document. There are
164     also some wrapper functions that correspond to the POSIX regular expression
165 ph10 691 API, but they do not give access to all the functionality. They are described
166     in the
167 nigel 75 <a href="pcreposix.html"><b>pcreposix</b></a>
168 nigel 77 documentation. Both of these APIs define a set of C function calls. A C++
169 ph10 691 wrapper is also distributed with PCRE. It is documented in the
170 nigel 77 <a href="pcrecpp.html"><b>pcrecpp</b></a>
171     page.
172 nigel 63 </P>
173     <P>
174 nigel 77 The native API C function prototypes are defined in the header file
175     <b>pcre.h</b>, and on Unix systems the library itself is called <b>libpcre</b>.
176     It can normally be accessed by adding <b>-lpcre</b> to the command for linking
177     an application that uses PCRE. The header file defines the macros PCRE_MAJOR
178     and PCRE_MINOR to contain the major and minor release numbers for the library.
179 nigel 75 Applications can use these to include support for different releases of PCRE.
180 nigel 63 </P>
181     <P>
182 ph10 535 In a Windows environment, if you want to statically link an application program
183     against a non-dll <b>pcre.a</b> file, you must define PCRE_STATIC before
184     including <b>pcre.h</b> or <b>pcrecpp.h</b>, because otherwise the
185     <b>pcre_malloc()</b> and <b>pcre_free()</b> exported functions will be declared
186     <b>__declspec(dllimport)</b>, with unwanted results.
187     </P>
188     <P>
189 nigel 77 The functions <b>pcre_compile()</b>, <b>pcre_compile2()</b>, <b>pcre_study()</b>,
190     and <b>pcre_exec()</b> are used for compiling and matching regular expressions
191     in a Perl-compatible manner. A sample program that demonstrates the simplest
192 ph10 429 way of using them is provided in the file called <i>pcredemo.c</i> in the PCRE
193     source distribution. A listing of this program is given in the
194     <a href="pcredemo.html"><b>pcredemo</b></a>
195     documentation, and the
196 nigel 75 <a href="pcresample.html"><b>pcresample</b></a>
197 ph10 313 documentation describes how to compile and run it.
198 nigel 63 </P>
199     <P>
200 ph10 691 Just-in-time compiler support is an optional feature of PCRE that can be built
201     in appropriate hardware environments. It greatly speeds up the matching
202     performance of many patterns. Simple programs can easily request that it be
203     used if available, by setting an option that is ignored when it is not
204     relevant. More complicated programs might need to make use of the functions
205     <b>pcre_jit_stack_alloc()</b>, <b>pcre_jit_stack_free()</b>, and
206     <b>pcre_assign_jit_stack()</b> in order to control the JIT code's memory usage.
207     These functions are discussed in the
208     <a href="pcrejit.html"><b>pcrejit</b></a>
209     documentation.
210     </P>
211     <P>
212 nigel 77 A second matching function, <b>pcre_dfa_exec()</b>, which is not
213     Perl-compatible, is also provided. This uses a different algorithm for the
214 nigel 91 matching. The alternative algorithm finds all possible matches (at a given
215 ph10 453 point in the subject), and scans the subject just once (unless there are
216     lookbehind assertions). However, this algorithm does not return captured
217     substrings. A description of the two matching algorithms and their advantages
218     and disadvantages is given in the
219 nigel 77 <a href="pcrematching.html"><b>pcrematching</b></a>
220     documentation.
221     </P>
222     <P>
223 nigel 75 In addition to the main compiling and matching functions, there are convenience
224 nigel 77 functions for extracting captured substrings from a subject string that is
225     matched by <b>pcre_exec()</b>. They are:
226 nigel 63 <pre>
227     <b>pcre_copy_substring()</b>
228     <b>pcre_copy_named_substring()</b>
229     <b>pcre_get_substring()</b>
230     <b>pcre_get_named_substring()</b>
231     <b>pcre_get_substring_list()</b>
232 nigel 75 <b>pcre_get_stringnumber()</b>
233 nigel 91 <b>pcre_get_stringtable_entries()</b>
234 nigel 75 </pre>
235 nigel 63 <b>pcre_free_substring()</b> and <b>pcre_free_substring_list()</b> are also
236     provided, to free the memory used for extracted strings.
237     </P>
238     <P>
239 nigel 75 The function <b>pcre_maketables()</b> is used to build a set of character tables
240 nigel 77 in the current locale for passing to <b>pcre_compile()</b>, <b>pcre_exec()</b>,
241     or <b>pcre_dfa_exec()</b>. This is an optional facility that is provided for
242     specialist use. Most commonly, no special tables are passed, in which case
243     internal tables that are generated when PCRE is built are used.
244 nigel 63 </P>
245     <P>
246     The function <b>pcre_fullinfo()</b> is used to find out information about a
247 nigel 75 compiled pattern; <b>pcre_info()</b> is an obsolete version that returns only
248 nigel 63 some of the available information, but is retained for backwards compatibility.
249     The function <b>pcre_version()</b> returns a pointer to a string containing the
250     version of PCRE and its date of release.
251     </P>
252     <P>
253 nigel 77 The function <b>pcre_refcount()</b> maintains a reference count in a data block
254     containing a compiled pattern. This is provided for the benefit of
255     object-oriented applications.
256     </P>
257     <P>
258 nigel 63 The global variables <b>pcre_malloc</b> and <b>pcre_free</b> initially contain
259 nigel 75 the entry points of the standard <b>malloc()</b> and <b>free()</b> functions,
260 nigel 63 respectively. PCRE calls the memory management functions via these variables,
261     so a calling program can replace them if it wishes to intercept the calls. This
262     should be done before calling any PCRE functions.
263     </P>
264     <P>
265 nigel 73 The global variables <b>pcre_stack_malloc</b> and <b>pcre_stack_free</b> are also
266     indirections to memory management functions. These special functions are used
267     only when PCRE is compiled to use the heap for remembering data, instead of
268 nigel 91 recursive function calls, when running the <b>pcre_exec()</b> function. See the
269     <a href="pcrebuild.html"><b>pcrebuild</b></a>
270     documentation for details of how to do this. It is a non-standard way of
271     building PCRE, for use in environments that have limited stacks. Because of the
272     greater use of memory management, it runs more slowly. Separate functions are
273     provided so that special-purpose external code can be used for this case. When
274     used, these functions are always called in a stack-like manner (last obtained,
275     first freed), and always for memory blocks of the same size. There is a
276     discussion about PCRE's stack usage in the
277     <a href="pcrestack.html"><b>pcrestack</b></a>
278     documentation.
279 nigel 73 </P>
280     <P>
281 nigel 63 The global variable <b>pcre_callout</b> initially contains NULL. It can be set
282     by the caller to a "callout" function, which PCRE will then call at specified
283 nigel 75 points during a matching operation. Details are given in the
284     <a href="pcrecallout.html"><b>pcrecallout</b></a>
285 nigel 63 documentation.
286 ph10 227 <a name="newlines"></a></P>
287 ph10 691 <br><a name="SEC5" href="#TOC1">NEWLINES</a><br>
288 nigel 63 <P>
289 ph10 150 PCRE supports five different conventions for indicating line breaks in
290 nigel 93 strings: a single CR (carriage return) character, a single LF (linefeed)
291 ph10 150 character, the two-character sequence CRLF, any of the three preceding, or any
292     Unicode newline sequence. The Unicode newline sequences are the three just
293     mentioned, plus the single characters VT (vertical tab, U+000B), FF (formfeed,
294     U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
295     (paragraph separator, U+2029).
296 nigel 93 </P>
297     <P>
298     Each of the first three conventions is used by at least one operating system as
299     its standard newline sequence. When PCRE is built, a default can be specified.
300     The default default is LF, which is the Unix standard. When PCRE is run, the
301     default can be overridden, either when a pattern is compiled, or when it is
302     matched.
303     </P>
304     <P>
305 ph10 227 At compile time, the newline convention can be specified by the <i>options</i>
306     argument of <b>pcre_compile()</b>, or it can be specified by special text at the
307     start of the pattern itself; this overrides any other settings. See the
308     <a href="pcrepattern.html"><b>pcrepattern</b></a>
309     page for details of the special character sequences.
310     </P>
311     <P>
312 nigel 91 In the PCRE documentation the word "newline" is used to mean "the character or
313 nigel 93 pair of characters that indicate a line break". The choice of newline
314     convention affects the handling of the dot, circumflex, and dollar
315     metacharacters, the handling of #-comments in /x mode, and, when CRLF is a
316     recognized line ending sequence, the match position advancement for a
317 ph10 227 non-anchored pattern. There is more detail about this in the
318     <a href="#execoptions">section on <b>pcre_exec()</b> options</a>
319 ph10 231 below.
320 nigel 91 </P>
321 ph10 231 <P>
322     The choice of newline convention does not affect the interpretation of
323     the \n or \r escape sequences, nor does it affect what \R matches, which is
324     controlled in a similar way, but by separate options.
325     </P>
326 ph10 691 <br><a name="SEC6" href="#TOC1">MULTITHREADING</a><br>
327 nigel 91 <P>
328 nigel 63 The PCRE functions can be used in multi-threading applications, with the
329 nigel 73 proviso that the memory management functions pointed to by <b>pcre_malloc</b>,
330     <b>pcre_free</b>, <b>pcre_stack_malloc</b>, and <b>pcre_stack_free</b>, and the
331     callout function pointed to by <b>pcre_callout</b>, are shared by all threads.
332 nigel 63 </P>
333     <P>
334     The compiled form of a regular expression is not altered during matching, so
335     the same compiled pattern can safely be used by several threads at once.
336     </P>
337     <P>
338 ph10 691 If the just-in-time optimization feature is being used, it needs separate
339     memory stack areas for each thread. See the
340     <a href="pcrejit.html"><b>pcrejit</b></a>
341     documentation for more details.
342     </P>
343     <br><a name="SEC7" href="#TOC1">SAVING PRECOMPILED PATTERNS FOR LATER USE</a><br>
344     <P>
345 nigel 75 The compiled form of a regular expression can be saved and re-used at a later
346     time, possibly by a different program, and even on a host other than the one on
347     which it was compiled. Details are given in the
348     <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
349 ph10 155 documentation. However, compiling a regular expression with one version of PCRE
350     for use with a different version is not guaranteed to work and may cause
351     crashes.
352 nigel 75 </P>
353 ph10 691 <br><a name="SEC8" href="#TOC1">CHECKING BUILD-TIME OPTIONS</a><br>
354 nigel 75 <P>
355 nigel 63 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
356     </P>
357     <P>
358     The function <b>pcre_config()</b> makes it possible for a PCRE client to
359     discover which optional features have been compiled into the PCRE library. The
360     <a href="pcrebuild.html"><b>pcrebuild</b></a>
361     documentation has more details about these optional features.
362     </P>
363     <P>
364     The first argument for <b>pcre_config()</b> is an integer, specifying which
365     information is required; the second argument is a pointer to a variable into
366     which the information is placed. The following information is available:
367     <pre>
369 nigel 75 </pre>
370 nigel 63 The output is an integer that is set to one if UTF-8 support is available;
371     otherwise it is set to zero.
372     <pre>
374     </pre>
375     The output is an integer that is set to one if support for Unicode character
376     properties is available; otherwise it is set to zero.
377     <pre>
378 ph10 691 PCRE_CONFIG_JIT
379     </pre>
380     The output is an integer that is set to one if support for just-in-time
381     compiling is available; otherwise it is set to zero.
382     <pre>
384 nigel 75 </pre>
385 nigel 91 The output is an integer whose value specifies the default character sequence
386 nigel 93 that is recognized as meaning "newline". The four values that are supported
387 ph10 392 are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and -1 for ANY.
388     Though they are derived from ASCII, the same values are returned in EBCDIC
389     environments. The default should normally correspond to the standard sequence
390     for your operating system.
391 nigel 63 <pre>
392 ph10 231 PCRE_CONFIG_BSR
393     </pre>
394     The output is an integer whose value indicates what character sequences the \R
395     escape sequence matches by default. A value of 0 means that \R matches any
396     Unicode line ending sequence; a value of 1 means that \R matches only CR, LF,
397     or CRLF. The default can be overridden when a pattern is compiled or matched.
398     <pre>
400 nigel 75 </pre>
401 nigel 63 The output is an integer that contains the number of bytes used for internal
402     linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
403     allow larger regular expressions to be compiled, at the expense of slower
404     matching. The default value of 2 is sufficient for all but the most massive
405     patterns, since it allows the compiled pattern to be up to 64K in size.
406     <pre>
408 nigel 75 </pre>
409 nigel 63 The output is an integer that contains the threshold above which the POSIX
410     interface uses <b>malloc()</b> for output vectors. Further details are given in
411 nigel 75 the
412     <a href="pcreposix.html"><b>pcreposix</b></a>
413     documentation.
414 nigel 63 <pre>
416 nigel 75 </pre>
417 ph10 392 The output is a long integer that gives the default limit for the number of
418 nigel 63 internal matching function calls in a <b>pcre_exec()</b> execution. Further
419     details are given with <b>pcre_exec()</b> below.
420 nigel 73 <pre>
422     </pre>
423 ph10 392 The output is a long integer that gives the default limit for the depth of
424 nigel 87 recursion when calling the internal matching function in a <b>pcre_exec()</b>
425     execution. Further details are given with <b>pcre_exec()</b> below.
426     <pre>
428 nigel 75 </pre>
429 nigel 77 The output is an integer that is set to one if internal recursion when running
430     <b>pcre_exec()</b> is implemented by recursive function calls that use the stack
431     to remember their state. This is the usual way that PCRE is compiled. The
432     output is zero if PCRE was compiled to use blocks of data on the heap instead
433     of recursive function calls. In this case, <b>pcre_stack_malloc</b> and
434     <b>pcre_stack_free</b> are called to manage memory blocks on the heap, thus
435     avoiding the use of the stack.
436 nigel 73 </P>
437 ph10 691 <br><a name="SEC9" href="#TOC1">COMPILING A PATTERN</a><br>
438 nigel 63 <P>
439     <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
440     <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
441     <b>const unsigned char *<i>tableptr</i>);</b>
442 nigel 77 <b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
443     <b>int *<i>errorcodeptr</i>,</b>
444     <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
445     <b>const unsigned char *<i>tableptr</i>);</b>
446 nigel 63 </P>
447     <P>
448 nigel 77 Either of the functions <b>pcre_compile()</b> or <b>pcre_compile2()</b> can be
449     called to compile a pattern into an internal form. The only difference between
450     the two interfaces is that <b>pcre_compile2()</b> has an additional argument,
451 ph10 461 <i>errorcodeptr</i>, via which a numerical error code can be returned. To avoid
452     too much repetition, we refer just to <b>pcre_compile()</b> below, but the
453     information applies equally to <b>pcre_compile2()</b>.
454 nigel 63 </P>
455     <P>
456 nigel 77 The pattern is a C string terminated by a binary zero, and is passed in the
457     <i>pattern</i> argument. A pointer to a single block of memory that is obtained
458     via <b>pcre_malloc</b> is returned. This contains the compiled code and related
459     data. The <b>pcre</b> type is defined for the returned block; this is a typedef
460     for a structure whose contents are not externally defined. It is up to the
461 nigel 91 caller to free the memory (via <b>pcre_free</b>) when it is no longer required.
462 nigel 77 </P>
463     <P>
464 nigel 63 Although the compiled code of a PCRE regex is relocatable, that is, it does not
465     depend on memory location, the complete <b>pcre</b> data block is not
466 nigel 75 fully relocatable, because it may contain a copy of the <i>tableptr</i>
467     argument, which is an address (see below).
468 nigel 63 </P>
469     <P>
470 nigel 93 The <i>options</i> argument contains various bit settings that affect the
471 nigel 75 compilation. It should be zero if no options are required. The available
472 ph10 416 options are described below. Some of them (in particular, those that are
473 ph10 461 compatible with Perl, but some others as well) can also be set and unset from
474 ph10 416 within the pattern (see the detailed description in the
475 nigel 75 <a href="pcrepattern.html"><b>pcrepattern</b></a>
476 ph10 416 documentation). For those options that can be different in different parts of
477 ph10 461 the pattern, the contents of the <i>options</i> argument specifies their
478     settings at the start of compilation and execution. The PCRE_ANCHORED,
479 ph10 579 PCRE_BSR_<i>xxx</i>, PCRE_NEWLINE_<i>xxx</i>, PCRE_NO_UTF8_CHECK, and
480     PCRE_NO_START_OPT options can be set at the time of matching as well as at
481     compile time.
482 nigel 63 </P>
483     <P>
484     If <i>errptr</i> is NULL, <b>pcre_compile()</b> returns NULL immediately.
485     Otherwise, if compilation of a pattern fails, <b>pcre_compile()</b> returns
486     NULL, and sets the variable pointed to by <i>errptr</i> to point to a textual
487 nigel 87 error message. This is a static string that is part of the library. You must
488 ph10 654 not try to free it. Normally, the offset from the start of the pattern to the
489     byte that was being processed when the error was discovered is placed in the
490     variable pointed to by <i>erroffset</i>, which must not be NULL (if it is, an
491     immediate error is given). However, for an invalid UTF-8 string, the offset is
492     that of the first byte of the failing character. Also, some errors are not
493     detected until checks are carried out when the whole pattern has been scanned;
494     in these cases the offset passed back is the length of the pattern.
495 nigel 63 </P>
496     <P>
497 ph10 572 Note that the offset is in bytes, not characters, even in UTF-8 mode. It may
498 ph10 654 sometimes point into the middle of a UTF-8 character.
499 ph10 572 </P>
500     <P>
501 nigel 77 If <b>pcre_compile2()</b> is used instead of <b>pcre_compile()</b>, and the
502     <i>errorcodeptr</i> argument is not NULL, a non-zero error code number is
503     returned via this argument in the event of an error. This is in addition to the
504     textual error message. Error codes and messages are listed below.
505     </P>
506     <P>
507 nigel 63 If the final argument, <i>tableptr</i>, is NULL, PCRE uses a default set of
508 nigel 75 character tables that are built when PCRE is compiled, using the default C
509     locale. Otherwise, <i>tableptr</i> must be an address that is the result of a
510     call to <b>pcre_maketables()</b>. This value is stored with the compiled
511     pattern, and used again by <b>pcre_exec()</b>, unless another table pointer is
512     passed to it. For more discussion, see the section on locale support below.
513 nigel 63 </P>
514     <P>
515     This code fragment shows a typical straightforward call to <b>pcre_compile()</b>:
516     <pre>
517     pcre *re;
518     const char *error;
519     int erroffset;
520     re = pcre_compile(
521     "^A.*Z", /* the pattern */
522     0, /* default options */
523     &error, /* for error message */
524     &erroffset, /* for error offset */
525     NULL); /* use default character tables */
526 nigel 75 </pre>
527     The following names for option bits are defined in the <b>pcre.h</b> header
528     file:
529 nigel 63 <pre>
531 nigel 75 </pre>
532 nigel 63 If this bit is set, the pattern is forced to be "anchored", that is, it is
533 nigel 75 constrained to match only at the first matching point in the string that is
534 nigel 63 being searched (the "subject string"). This effect can also be achieved by
535     appropriate constructs in the pattern itself, which is the only way to do it in
536     Perl.
537     <pre>
538 nigel 75 PCRE_AUTO_CALLOUT
539     </pre>
540     If this bit is set, <b>pcre_compile()</b> automatically inserts callout items,
541     all with number 255, before each pattern item. For discussion of the callout
542     facility, see the
543     <a href="pcrecallout.html"><b>pcrecallout</b></a>
544     documentation.
545     <pre>
546 ph10 231 PCRE_BSR_ANYCRLF
548     </pre>
549     These options (which are mutually exclusive) control what the \R escape
550     sequence matches. The choice is either to match only CR, LF, or CRLF, or to
551     match any Unicode newline sequence. The default is specified when PCRE is
552     built. It can be overridden from within the pattern, or by setting an option
553     when a compiled pattern is matched.
554     <pre>
555 nigel 63 PCRE_CASELESS
556 nigel 75 </pre>
557 nigel 63 If this bit is set, letters in the pattern match both upper and lower case
558     letters. It is equivalent to Perl's /i option, and it can be changed within a
559 nigel 77 pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
560     concept of case for characters whose values are less than 128, so caseless
561     matching is always possible. For characters with higher values, the concept of
562     case is supported if PCRE is compiled with Unicode property support, but not
563     otherwise. If you want to use caseless matching for characters 128 and above,
564     you must ensure that PCRE is compiled with Unicode property support as well as
565     with UTF-8 support.
566 nigel 63 <pre>
568 nigel 75 </pre>
569 nigel 63 If this bit is set, a dollar metacharacter in the pattern matches only at the
570     end of the subject string. Without this option, a dollar also matches
571 nigel 91 immediately before a newline at the end of the string (but not before any other
572     newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
573     There is no equivalent to this option in Perl, and no way to set it within a
574     pattern.
575 nigel 63 <pre>
577 nigel 75 </pre>
578 ph10 572 If this bit is set, a dot metacharacter in the pattern matches a character of
579     any value, including one that indicates a newline. However, it only ever
580     matches one character, even if newlines are coded as CRLF. Without this option,
581     a dot does not match when the current position is at a newline. This option is
582     equivalent to Perl's /s option, and it can be changed within a pattern by a
583     (?s) option setting. A negative class such as [^a] always matches newline
584     characters, independent of the setting of this option.
585 nigel 63 <pre>
586 nigel 91 PCRE_DUPNAMES
587     </pre>
588     If this bit is set, names used to identify capturing subpatterns need not be
589     unique. This can be helpful for certain types of pattern when it is known that
590     only one instance of the named subpattern can ever be matched. There are more
591     details of named subpatterns below; see also the
592     <a href="pcrepattern.html"><b>pcrepattern</b></a>
593     documentation.
594     <pre>
595 nigel 63 PCRE_EXTENDED
596 nigel 75 </pre>
597 nigel 63 If this bit is set, whitespace data characters in the pattern are totally
598     ignored except when escaped or inside a character class. Whitespace does not
599     include the VT character (code 11). In addition, characters between an
600 nigel 91 unescaped # outside a character class and the next newline, inclusive, are also
601     ignored. This is equivalent to Perl's /x option, and it can be changed within a
602     pattern by a (?x) option setting.
603 nigel 63 </P>
604     <P>
605 ph10 654 Which characters are interpreted as newlines is controlled by the options
606     passed to <b>pcre_compile()</b> or by a special sequence at the start of the
607     pattern, as described in the section entitled
608 ph10 572 <a href="pcrepattern.html#newlines">"Newline conventions"</a>
609     in the <b>pcrepattern</b> documentation. Note that the end of this type of
610     comment is a literal newline sequence in the pattern; escape sequences that
611     happen to represent a newline do not count.
612     </P>
613     <P>
614 nigel 63 This option makes it possible to include comments inside complicated patterns.
615     Note, however, that this applies only to data characters. Whitespace characters
616     may never appear within special character sequences in a pattern, for example
617 ph10 572 within the sequence (?( that introduces a conditional subpattern.
618 nigel 63 <pre>
619     PCRE_EXTRA
620 nigel 75 </pre>
621 nigel 63 This option was invented in order to turn on additional functionality of PCRE
622     that is incompatible with Perl, but it is currently of very little use. When
623     set, any backslash in a pattern that is followed by a letter that has no
624     special meaning causes an error, thus reserving these combinations for future
625     expansion. By default, as in Perl, a backslash followed by a letter with no
626 nigel 91 special meaning is treated as a literal. (Perl can, however, be persuaded to
627 ph10 518 give an error for this, by running it with the -w option.) There are at present
628     no other features controlled by this option. It can also be set by a (?X)
629     option setting within a pattern.
630 nigel 63 <pre>
631 nigel 77 PCRE_FIRSTLINE
632     </pre>
633     If this option is set, an unanchored pattern is required to match before or at
634 nigel 91 the first newline in the subject string, though the matched text may continue
635     over the newline.
636 nigel 77 <pre>
638     </pre>
639     If this option is set, PCRE's behaviour is changed in some ways so that it is
640     compatible with JavaScript rather than Perl. The changes are as follows:
641     </P>
642     <P>
643     (1) A lone closing square bracket in a pattern causes a compile-time error,
644     because this is illegal in JavaScript (by default it is treated as a data
645     character). Thus, the pattern AB]CD becomes illegal when this option is set.
646     </P>
647     <P>
648     (2) At run time, a back reference to an unset subpattern group matches an empty
649     string (by default this causes the current matching alternative to fail). A
650     pattern such as (\1)(a) succeeds when this option is set (assuming it can find
651     an "a" in the subject), whereas it fails by default, for Perl compatibility.
652 ph10 784 </P>
653     <P>
654 ph10 788 (3) \U matches an upper case "U" character; by default \U causes a compile
655 ph10 784 time error (Perl uses \U to upper case subsequent characters).
656     </P>
657     <P>
658 ph10 788 (4) \u matches a lower case "u" character unless it is followed by four
659     hexadecimal digits, in which case the hexadecimal number defines the code point
660     to match. By default, \u causes a compile time error (Perl uses it to upper
661 ph10 784 case the following character).
662     </P>
663     <P>
664 ph10 788 (5) \x matches a lower case "x" character unless it is followed by two
665     hexadecimal digits, in which case the hexadecimal number defines the code point
666     to match. By default, as in Perl, a hexadecimal number is always expected after
667     \x, but it may have zero, one, or two digits (so, for example, \xz matches a
668 ph10 784 binary zero character followed by z).
669 ph10 345 <pre>
670 nigel 63 PCRE_MULTILINE
671 nigel 75 </pre>
672     By default, PCRE treats the subject string as consisting of a single line of
673     characters (even if it actually contains newlines). The "start of line"
674 nigel 63 metacharacter (^) matches only at the start of the string, while the "end of
675     line" metacharacter ($) matches only at the end of the string, or before a
676     terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
677     Perl.
678     </P>
679     <P>
680     When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
681 nigel 91 match immediately following or immediately before internal newlines in the
682     subject string, respectively, as well as at the very start and end. This is
683     equivalent to Perl's /m option, and it can be changed within a pattern by a
684     (?m) option setting. If there are no newlines in a subject string, or no
685 nigel 63 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
686     <pre>
687 nigel 91 PCRE_NEWLINE_CR
691 nigel 93 PCRE_NEWLINE_ANY
692 nigel 91 </pre>
693     These options override the default newline definition that was chosen when PCRE
694     was built. Setting the first or the second specifies that a newline is
695 nigel 93 indicated by a single character (CR or LF, respectively). Setting
696     PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character
697 ph10 150 CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three
698     preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies
699     that any Unicode newline sequence should be recognized. The Unicode newline
700     sequences are the three just mentioned, plus the single characters VT (vertical
701     tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line
702     separator, U+2028), and PS (paragraph separator, U+2029). The last two are
703     recognized only in UTF-8 mode.
704 nigel 91 </P>
705     <P>
706 nigel 93 The newline setting in the options word uses three bits that are treated
707 ph10 150 as a number, giving eight possibilities. Currently only six are used (default
708     plus the five values above). This means that if you set more than one newline
709 nigel 93 option, the combination may or may not be sensible. For example,
710     PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to PCRE_NEWLINE_CRLF, but
711 ph10 150 other combinations may yield unused numbers and cause an error.
712 nigel 93 </P>
713     <P>
714 ph10 572 The only time that a line break in a pattern is specially recognized when
715     compiling is when PCRE_EXTENDED is set. CR and LF are whitespace characters,
716     and so are ignored in this mode. Also, an unescaped # outside a character class
717     indicates a comment that lasts until after the next line break sequence. In
718     other circumstances, line break sequences in patterns are treated as literal
719     data.
720 nigel 93 </P>
721     <P>
722     The newline option that is set at compile time becomes the default that is used
723     for <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, but it can be overridden.
724 nigel 91 <pre>
726 nigel 75 </pre>
727 nigel 63 If this option is set, it disables the use of numbered capturing parentheses in
728     the pattern. Any opening parenthesis that is not followed by ? behaves as if it
729     were followed by ?: but named parentheses can still be used for capturing (and
730     they acquire numbers in the usual way). There is no equivalent of this option
731     in Perl.
732     <pre>
733 ph10 579 NO_START_OPTIMIZE
734     </pre>
735     This is an option that acts at matching time; that is, it is really an option
736     for <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>. If it is set at compile time,
737     it is remembered with the compiled pattern and assumed at matching time. For
738     details see the discussion of PCRE_NO_START_OPTIMIZE
739     <a href="#execoptions">below.</a>
740     <pre>
741 ph10 535 PCRE_UCP
742     </pre>
743 ph10 572 This option changes the way PCRE processes \B, \b, \D, \d, \S, \s, \W,
744     \w, and some of the POSIX character classes. By default, only ASCII characters
745     are recognized, but if PCRE_UCP is set, Unicode properties are used instead to
746     classify characters. More details are given in the section on
747 ph10 535 <a href="pcre.html#genericchartypes">generic character types</a>
748     in the
749     <a href="pcrepattern.html"><b>pcrepattern</b></a>
750     page. If you set PCRE_UCP, matching one of the items it affects takes much
751     longer. The option is available only if PCRE has been compiled with Unicode
752     property support.
753     <pre>
754 nigel 63 PCRE_UNGREEDY
755 nigel 75 </pre>
756 nigel 63 This option inverts the "greediness" of the quantifiers so that they are not
757     greedy by default, but become greedy if followed by "?". It is not compatible
758     with Perl. It can also be set by a (?U) option setting within the pattern.
759     <pre>
760     PCRE_UTF8
761 nigel 75 </pre>
762 nigel 63 This option causes PCRE to regard both the pattern and the subject as strings
763     of UTF-8 characters instead of single-byte character strings. However, it is
764 nigel 75 available only when PCRE is built to include UTF-8 support. If not, the use
765 nigel 63 of this option provokes an error. Details of how this option changes the
766     behaviour of PCRE are given in the
767 ph10 678 <a href="pcreunicode.html"><b>pcreunicode</b></a>
768 nigel 63 page.
769 nigel 71 <pre>
771 nigel 75 </pre>
772 nigel 71 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
773 ph10 211 automatically checked. There is a discussion about the
774     <a href="pcre.html#utf8strings">validity of UTF-8 strings</a>
775     in the main
776     <a href="pcre.html"><b>pcre</b></a>
777     page. If an invalid UTF-8 sequence of bytes is found, <b>pcre_compile()</b>
778     returns an error. If you already know that your pattern is valid, and you want
779     to skip this check for performance reasons, you can set the PCRE_NO_UTF8_CHECK
780     option. When it is set, the effect of passing an invalid UTF-8 string as a
781     pattern is undefined. It may cause your program to crash. Note that this option
782     can also be passed to <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, to suppress
783     the UTF-8 validity checking of subject strings.
784 nigel 71 </P>
785 ph10 691 <br><a name="SEC10" href="#TOC1">COMPILATION ERROR CODES</a><br>
786 nigel 63 <P>
787 nigel 77 The following table lists the error codes than may be returned by
788     <b>pcre_compile2()</b>, along with the error messages that may be returned by
789 nigel 93 both compiling functions. As PCRE has developed, some error codes have fallen
790     out of use. To avoid confusion, they have not been re-used.
791 nigel 77 <pre>
792     0 no error
793     1 \ at end of pattern
794     2 \c at end of pattern
795     3 unrecognized character follows \
796     4 numbers out of order in {} quantifier
797     5 number too big in {} quantifier
798     6 missing terminating ] for character class
799     7 invalid escape sequence in character class
800     8 range out of order in character class
801     9 nothing to repeat
802 nigel 93 10 [this code is not in use]
803 nigel 77 11 internal error: unexpected repeat
804 ph10 292 12 unrecognized character after (? or (?-
805 nigel 77 13 POSIX named classes are supported only within a class
806     14 missing )
807     15 reference to non-existent subpattern
808     16 erroffset passed as NULL
809     17 unknown option bit(s) set
810     18 missing ) after comment
811 nigel 93 19 [this code is not in use]
812 ph10 292 20 regular expression is too large
813 nigel 77 21 failed to get memory
814     22 unmatched parentheses
815     23 internal error: code overflow
816     24 unrecognized character after (?&#60;
817     25 lookbehind assertion is not fixed length
818 nigel 91 26 malformed number or name after (?(
819 nigel 77 27 conditional group contains more than two branches
820     28 assertion expected after (?(
821 ph10 182 29 (?R or (?[+-]digits must be followed by )
822 nigel 77 30 unknown POSIX class name
823     31 POSIX collating elements are not supported
824     32 this version of PCRE is not compiled with PCRE_UTF8 support
825 nigel 93 33 [this code is not in use]
826 nigel 77 34 character value in \x{...} sequence is too large
827     35 invalid condition (?(0)
828     36 \C not allowed in lookbehind assertion
829 ph10 656 37 PCRE does not support \L, \l, \N{name}, \U, or \u
830 nigel 77 38 number after (?C is &#62; 255
831     39 closing ) for (?C expected
832     40 recursive call could loop indefinitely
833     41 unrecognized character after (?P
834 nigel 93 42 syntax error in subpattern name (missing terminator)
835 nigel 91 43 two named subpatterns have the same name
836 nigel 77 44 invalid UTF-8 string
837     45 support for \P, \p, and \X has not been compiled
838     46 malformed \P or \p sequence
839     47 unknown property name after \P or \p
840 nigel 91 48 subpattern name is too long (maximum 32 characters)
841 ph10 292 49 too many named subpatterns (maximum 10000)
842 ph10 202 50 [this code is not in use]
843 nigel 91 51 octal value is greater than \377 (not in UTF-8 mode)
844 nigel 93 52 internal error: overran compiling workspace
845 ph10 548 53 internal error: previously-checked referenced subpattern
846     not found
847 nigel 93 54 DEFINE group contains more than one branch
848     55 repeating a DEFINE group is not allowed
849 ph10 231 56 inconsistent NEWLINE options
850 ph10 345 57 \g is not followed by a braced, angle-bracketed, or quoted
851     name/number or by a plain number
852     58 a numbered reference must not be zero
853 ph10 512 59 an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
854 ph10 292 60 (*VERB) not recognized
855     61 number is too big
856     62 subpattern name expected
857     63 digit expected after (?+
858 ph10 345 64 ] is an invalid data character in JavaScript compatibility mode
859 ph10 548 65 different names for subpatterns of the same number are
860     not allowed
861 ph10 512 66 (*MARK) must have an argument
862 ph10 535 67 this version of PCRE is not compiled with PCRE_UCP support
863 ph10 656 68 \c must be followed by an ASCII character
864 ph10 659 69 \k is not followed by a braced, angle-bracketed, or quoted name
865 ph10 292 </pre>
866     The numbers 32 and 10000 in errors 48 and 49 are defaults; different values may
867     be used if the limits were changed when PCRE was built.
868 ph10 656 <a name="studyingapattern"></a></P>
869 ph10 691 <br><a name="SEC11" href="#TOC1">STUDYING A PATTERN</a><br>
870 nigel 77 <P>
871     <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i></b>
872 nigel 63 <b>const char **<i>errptr</i>);</b>
873     </P>
874     <P>
875 nigel 75 If a compiled pattern is going to be used several times, it is worth spending
876     more time analyzing it in order to speed up the time taken for matching. The
877 nigel 63 function <b>pcre_study()</b> takes a pointer to a compiled pattern as its first
878 nigel 75 argument. If studying the pattern produces additional information that will
879     help speed up matching, <b>pcre_study()</b> returns a pointer to a
880     <b>pcre_extra</b> block, in which the <i>study_data</i> field points to the
881     results of the study.
882 nigel 63 </P>
883     <P>
884 nigel 75 The returned value from <b>pcre_study()</b> can be passed directly to
885 ph10 461 <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>. However, a <b>pcre_extra</b> block
886     also contains other fields that can be set by the caller before the block is
887     passed; these are described
888 nigel 75 <a href="#extradata">below</a>
889     in the section on matching a pattern.
890 nigel 63 </P>
891     <P>
892 ph10 461 If studying the pattern does not produce any useful information,
893 nigel 75 <b>pcre_study()</b> returns NULL. In that circumstance, if the calling program
894 ph10 461 wants to pass any of the other fields to <b>pcre_exec()</b> or
895     <b>pcre_dfa_exec()</b>, it must set up its own <b>pcre_extra</b> block.
896 nigel 63 </P>
897     <P>
898 ph10 691 The second argument of <b>pcre_study()</b> contains option bits. There is only
899     one option: PCRE_STUDY_JIT_COMPILE. If this is set, and the just-in-time
900     compiler is available, the pattern is further compiled into machine code that
901     executes much faster than the <b>pcre_exec()</b> matching function. If
902     the just-in-time compiler is not available, this option is ignored. All other
903     bits in the <i>options</i> argument must be zero.
904 nigel 75 </P>
905     <P>
906 ph10 691 JIT compilation is a heavyweight optimization. It can take some time for
907     patterns to be analyzed, and for one-off matches and simple patterns the
908     benefit of faster execution might be offset by a much slower study time.
909     Not all patterns can be optimized by the JIT compiler. For those that cannot be
910     handled, matching automatically falls back to the <b>pcre_exec()</b>
911     interpreter. For more details, see the
912     <a href="pcrejit.html"><b>pcrejit</b></a>
913     documentation.
914     </P>
915     <P>
916 nigel 63 The third argument for <b>pcre_study()</b> is a pointer for an error message. If
917     studying succeeds (even if no data is returned), the variable it points to is
918 nigel 87 set to NULL. Otherwise it is set to point to a textual error message. This is a
919     static string that is part of the library. You must not try to free it. You
920     should test the error pointer for NULL after calling <b>pcre_study()</b>, to be
921     sure that it has run successfully.
922 nigel 63 </P>
923     <P>
924 ph10 691 When you are finished with a pattern, you can free the memory used for the
925     study data by calling <b>pcre_free_study()</b>. This function was added to the
926     API for release 8.20. For earlier versions, the memory could be freed with
927     <b>pcre_free()</b>, just like the pattern itself. This will still work in cases
928     where PCRE_STUDY_JIT_COMPILE is not used, but it is advisable to change to the
929     new function when convenient.
930     </P>
931     <P>
932     This is a typical way in which <b>pcre_study</b>() is used (except that in a
933     real application there should be tests for errors):
934 nigel 63 <pre>
935 ph10 691 int rc;
936     pcre *re;
937     pcre_extra *sd;
938     re = pcre_compile("pattern", 0, &error, &erroroffset, NULL);
939     sd = pcre_study(
940 nigel 63 re, /* result of pcre_compile() */
941 ph10 691 0, /* no options */
942 nigel 63 &error); /* set to NULL or points to a message */
943 ph10 691 rc = pcre_exec( /* see below for details of pcre_exec() options */
944     re, sd, "subject", 7, 0, 0, ovector, 30);
945     ...
946     pcre_free_study(sd);
947     pcre_free(re);
948 nigel 75 </pre>
949 ph10 461 Studying a pattern does two things: first, a lower bound for the length of
950     subject string that is needed to match the pattern is computed. This does not
951     mean that there are any strings of that length that match, but it does
952     guarantee that no shorter strings match. The value is used by
953     <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b> to avoid wasting time by trying to
954     match strings that are shorter than the lower bound. You can find out the value
955     in a calling program via the <b>pcre_fullinfo()</b> function.
956     </P>
957     <P>
958     Studying a pattern is also useful for non-anchored patterns that do not have a
959     single fixed starting character. A bitmap of possible starting bytes is
960     created. This speeds up finding a position in the subject at which to start
961     matching.
962 ph10 548 </P>
963     <P>
964 ph10 691 These two optimizations apply to both <b>pcre_exec()</b> and
965     <b>pcre_dfa_exec()</b>. However, they are not used by <b>pcre_exec()</b> if
966     <b>pcre_study()</b> is called with the PCRE_STUDY_JIT_COMPILE option, and
967     just-in-time compiling is successful. The optimizations can be disabled by
968     setting the PCRE_NO_START_OPTIMIZE option when calling <b>pcre_exec()</b> or
969 ph10 548 <b>pcre_dfa_exec()</b>. You might want to do this if your pattern contains
970 ph10 691 callouts or (*MARK) (which cannot be handled by the JIT compiler), and you want
971     to make use of these facilities in cases where matching fails. See the
972     discussion of PCRE_NO_START_OPTIMIZE
973 ph10 548 <a href="#execoptions">below.</a>
974 nigel 75 <a name="localesupport"></a></P>
975 ph10 691 <br><a name="SEC12" href="#TOC1">LOCALE SUPPORT</a><br>
976 nigel 63 <P>
977 ph10 142 PCRE handles caseless matching, and determines whether characters are letters,
978 nigel 75 digits, or whatever, by reference to a set of tables, indexed by character
979 nigel 77 value. When running in UTF-8 mode, this applies only to characters with codes
980 ph10 535 less than 128. By default, higher-valued codes never match escapes such as \w
981     or \d, but they can be tested with \p if PCRE is built with Unicode character
982     property support. Alternatively, the PCRE_UCP option can be set at compile
983     time; this causes \w and friends to use Unicode property support instead of
984     built-in tables. The use of locales with Unicode is discouraged. If you are
985     handling characters with codes greater than 128, you should either use UTF-8
986     and Unicode, or use locales, but not try to mix the two.
987 nigel 63 </P>
988     <P>
989 ph10 142 PCRE contains an internal set of tables that are used when the final argument
990     of <b>pcre_compile()</b> is NULL. These are sufficient for many applications.
991     Normally, the internal tables recognize only ASCII characters. However, when
992     PCRE is built, it is possible to cause the internal tables to be rebuilt in the
993     default "C" locale of the local system, which may cause them to be different.
994 nigel 63 </P>
995     <P>
996 ph10 142 The internal tables can always be overridden by tables supplied by the
997     application that calls PCRE. These may be created in a different locale from
998     the default. As more and more applications change to using Unicode, the need
999     for this locale support is expected to die away.
1000     </P>
1001     <P>
1002 nigel 75 External tables are built by calling the <b>pcre_maketables()</b> function,
1003     which has no arguments, in the relevant locale. The result can then be passed
1004     to <b>pcre_compile()</b> or <b>pcre_exec()</b> as often as necessary. For
1005     example, to build and use tables that are appropriate for the French locale
1006     (where accented characters with values greater than 128 are treated as letters),
1007     the following code could be used:
1008 nigel 63 <pre>
1009 nigel 75 setlocale(LC_CTYPE, "fr_FR");
1010 nigel 63 tables = pcre_maketables();
1011     re = pcre_compile(..., tables);
1012 nigel 75 </pre>
1013 ph10 142 The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
1014     are using Windows, the name for the French locale is "french".
1015     </P>
1016     <P>
1017 nigel 75 When <b>pcre_maketables()</b> runs, the tables are built in memory that is
1018     obtained via <b>pcre_malloc</b>. It is the caller's responsibility to ensure
1019     that the memory containing the tables remains available for as long as it is
1020     needed.
1021 nigel 63 </P>
1022     <P>
1023 nigel 75 The pointer that is passed to <b>pcre_compile()</b> is saved with the compiled
1024 nigel 63 pattern, and the same tables are used via this pointer by <b>pcre_study()</b>
1025 nigel 75 and normally also by <b>pcre_exec()</b>. Thus, by default, for any single
1026     pattern, compilation, studying and matching all happen in the same locale, but
1027     different patterns can be compiled in different locales.
1028 nigel 63 </P>
1029     <P>
1030 nigel 75 It is possible to pass a table pointer or NULL (indicating the use of the
1031     internal tables) to <b>pcre_exec()</b>. Although not intended for this purpose,
1032     this facility could be used to match a pattern in a different locale from the
1033     one in which it was compiled. Passing table pointers at run time is discussed
1034     below in the section on matching a pattern.
1035 ph10 654 <a name="infoaboutpattern"></a></P>
1036 ph10 691 <br><a name="SEC13" href="#TOC1">INFORMATION ABOUT A PATTERN</a><br>
1037 nigel 75 <P>
1038 nigel 63 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1039     <b>int <i>what</i>, void *<i>where</i>);</b>
1040     </P>
1041     <P>
1042     The <b>pcre_fullinfo()</b> function returns information about a compiled
1043     pattern. It replaces the obsolete <b>pcre_info()</b> function, which is
1044     nevertheless retained for backwards compability (and is documented below).
1045     </P>
1046     <P>
1047     The first argument for <b>pcre_fullinfo()</b> is a pointer to the compiled
1048     pattern. The second argument is the result of <b>pcre_study()</b>, or NULL if
1049     the pattern was not studied. The third argument specifies which piece of
1050     information is required, and the fourth argument is a pointer to a variable
1051     to receive the data. The yield of the function is zero for success, or one of
1052     the following negative numbers:
1053     <pre>
1054     PCRE_ERROR_NULL the argument <i>code</i> was NULL
1055     the argument <i>where</i> was NULL
1056     PCRE_ERROR_BADMAGIC the "magic number" was not found
1057     PCRE_ERROR_BADOPTION the value of <i>what</i> was invalid
1058 nigel 75 </pre>
1059     The "magic number" is placed at the start of each compiled pattern as an simple
1060     check against passing an arbitrary memory pointer. Here is a typical call of
1061     <b>pcre_fullinfo()</b>, to obtain the length of the compiled pattern:
1062 nigel 63 <pre>
1063     int rc;
1064 nigel 91 size_t length;
1065 nigel 63 rc = pcre_fullinfo(
1066     re, /* result of pcre_compile() */
1067 ph10 691 sd, /* result of pcre_study(), or NULL */
1068 nigel 63 PCRE_INFO_SIZE, /* what is required */
1069     &length); /* where to put the data */
1070 nigel 75 </pre>
1071 nigel 63 The possible values for the third argument are defined in <b>pcre.h</b>, and are
1072     as follows:
1073     <pre>
1075 nigel 75 </pre>
1076 nigel 63 Return the number of the highest back reference in the pattern. The fourth
1077     argument should point to an <b>int</b> variable. Zero is returned if there are
1078     no back references.
1079     <pre>
1081 nigel 75 </pre>
1082 nigel 63 Return the number of capturing subpatterns in the pattern. The fourth argument
1083 nigel 75 should point to an <b>int</b> variable.
1084 nigel 63 <pre>
1086 nigel 75 </pre>
1087     Return a pointer to the internal default character tables within PCRE. The
1088     fourth argument should point to an <b>unsigned char *</b> variable. This
1089     information call is provided for internal use by the <b>pcre_study()</b>
1090     function. External callers can cause PCRE to use its internal tables by passing
1091     a NULL table pointer.
1092     <pre>
1094 nigel 75 </pre>
1095 nigel 63 Return information about the first byte of any matched string, for a
1096 nigel 91 non-anchored pattern. The fourth argument should point to an <b>int</b>
1097     variable. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name is
1098     still recognized for backwards compatibility.)
1099 nigel 63 </P>
1100     <P>
1101 nigel 75 If there is a fixed first byte, for example, from a pattern such as
1102 nigel 93 (cat|cow|coyote), its value is returned. Otherwise, if either
1103 nigel 75 <br>
1104     <br>
1105 nigel 63 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
1106     starts with "^", or
1107 nigel 75 <br>
1108     <br>
1109 nigel 63 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
1110     (if it were set, the pattern would be anchored),
1111 nigel 75 <br>
1112     <br>
1113 nigel 63 -1 is returned, indicating that the pattern matches only at the start of a
1114     subject string or after any newline within the string. Otherwise -2 is
1115     returned. For anchored patterns, -2 is returned.
1116     <pre>
1118 nigel 75 </pre>
1119 nigel 63 If the pattern was studied, and this resulted in the construction of a 256-bit
1120     table indicating a fixed set of bytes for the first byte in any matching
1121     string, a pointer to the table is returned. Otherwise NULL is returned. The
1122     fourth argument should point to an <b>unsigned char *</b> variable.
1123     <pre>
1125     </pre>
1126     Return 1 if the pattern contains any explicit matches for CR or LF characters,
1127 ph10 243 otherwise 0. The fourth argument should point to an <b>int</b> variable. An
1128     explicit match is either a literal CR or LF character, or \r or \n.
1129 ph10 227 <pre>
1130 ph10 172 PCRE_INFO_JCHANGED
1131     </pre>
1132 ph10 286 Return 1 if the (?J) or (?-J) option setting is used in the pattern, otherwise
1133     0. The fourth argument should point to an <b>int</b> variable. (?J) and
1134     (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1135 ph10 172 <pre>
1136 ph10 691 PCRE_INFO_JIT
1137     </pre>
1138     Return 1 if the pattern was studied with the PCRE_STUDY_JIT_COMPILE option, and
1139     just-in-time compiling was successful. The fourth argument should point to an
1140     <b>int</b> variable. A return value of 0 means that JIT support is not available
1141     in this version of PCRE, or that the pattern was not studied with the
1142     PCRE_STUDY_JIT_COMPILE option, or that the JIT compiler could not handle this
1143     particular pattern. See the
1144     <a href="pcrejit.html"><b>pcrejit</b></a>
1145     documentation for details of what can and cannot be handled.
1146     <pre>
1147 ph10 784 PCRE_INFO_JITSIZE
1148     </pre>
1149     If the pattern was successfully studied with the PCRE_STUDY_JIT_COMPILE option,
1150     return the size of the JIT compiled code, otherwise return zero. The fourth
1151     argument should point to a <b>size_t</b> variable.
1152     <pre>
1154 nigel 75 </pre>
1155 nigel 65 Return the value of the rightmost literal byte that must exist in any matched
1156     string, other than at its start, if such a byte has been recorded. The fourth
1157     argument should point to an <b>int</b> variable. If there is no such byte, -1 is
1158     returned. For anchored patterns, a last literal byte is recorded only if it
1159     follows something of variable length. For example, for the pattern
1160     /^a\d+z\d+/ the returned value is "z", but for /^a\dz\d/ the returned value
1161     is -1.
1162 nigel 63 <pre>
1164     </pre>
1165     If the pattern was studied and a minimum length for matching subject strings
1166     was computed, its value is returned. Otherwise the returned value is -1. The
1167     value is a number of characters, not bytes (this may be relevant in UTF-8
1168     mode). The fourth argument should point to an <b>int</b> variable. A
1169     non-negative value is a lower bound to the length of any matching string. There
1170     may not be any strings of that length that do actually match, but every string
1171     that does match is at least that long.
1172     <pre>
1176 nigel 75 </pre>
1177 nigel 63 PCRE supports the use of named as well as numbered capturing parentheses. The
1178     names are just an additional way of identifying the parentheses, which still
1179 nigel 91 acquire numbers. Several convenience functions such as
1180     <b>pcre_get_named_substring()</b> are provided for extracting captured
1181     substrings by name. It is also possible to extract the data directly, by first
1182     converting the name to a number in order to access the correct pointers in the
1183     output vector (described with <b>pcre_exec()</b> below). To do the conversion,
1184     you need to use the name-to-number map, which is described by these three
1185     values.
1186 nigel 63 </P>
1187     <P>
1188     The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
1189     the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
1190     entry; both of these return an <b>int</b> value. The entry size depends on the
1191     length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
1192     entry of the table (a pointer to <b>char</b>). The first two bytes of each entry
1193     are the number of the capturing parenthesis, most significant byte first. The
1194 ph10 461 rest of the entry is the corresponding name, zero terminated.
1195     </P>
1196     <P>
1197     The names are in alphabetical order. Duplicate names may appear if (?| is used
1198     to create multiple groups with the same number, as described in the
1199     <a href="pcrepattern.html#dupsubpatternnumber">section on duplicate subpattern numbers</a>
1200     in the
1201     <a href="pcrepattern.html"><b>pcrepattern</b></a>
1202     page. Duplicate names for subpatterns with different numbers are permitted only
1203     if PCRE_DUPNAMES is set. In all cases of duplicate names, they appear in the
1204     table in the order in which they were found in the pattern. In the absence of
1205     (?| this is the order of increasing number; when (?| is used this is not
1206     necessarily the case because later subpatterns may have lower numbers.
1207     </P>
1208     <P>
1209     As a simple example of the name/number table, consider the following pattern
1210     (assume PCRE_EXTENDED is set, so white space - including newlines - is
1211     ignored):
1212 nigel 63 <pre>
1213 nigel 93 (?&#60;date&#62; (?&#60;year&#62;(\d\d)?\d\d) - (?&#60;month&#62;\d\d) - (?&#60;day&#62;\d\d) )
1214 nigel 75 </pre>
1215 nigel 63 There are four named subpatterns, so the table has four entries, and each entry
1216     in the table is eight bytes long. The table is as follows, with non-printing
1217 nigel 75 bytes shows in hexadecimal, and undefined bytes shown as ??:
1218 nigel 63 <pre>
1219     00 01 d a t e 00 ??
1220     00 05 d a y 00 ?? ??
1221     00 04 m o n t h 00
1222     00 02 y e a r 00 ??
1223 nigel 75 </pre>
1224     When writing code to extract data from named subpatterns using the
1225 nigel 91 name-to-number map, remember that the length of the entries is likely to be
1226 nigel 75 different for each compiled pattern.
1227 nigel 63 <pre>
1229     </pre>
1230 ph10 453 Return 1 if the pattern can be used for partial matching with
1231     <b>pcre_exec()</b>, otherwise 0. The fourth argument should point to an
1232     <b>int</b> variable. From release 8.00, this always returns 1, because the
1233     restrictions that previously applied to partial matching have been lifted. The
1234 ph10 172 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1235 ph10 429 documentation gives details of partial matching.
1236 ph10 172 <pre>
1237 nigel 63 PCRE_INFO_OPTIONS
1238 nigel 75 </pre>
1239 nigel 63 Return a copy of the options with which the pattern was compiled. The fourth
1240     argument should point to an <b>unsigned long int</b> variable. These option bits
1241     are those specified in the call to <b>pcre_compile()</b>, modified by any
1242 ph10 197 top-level option settings at the start of the pattern itself. In other words,
1243     they are the options that will be in force when matching starts. For example,
1244     if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED option, the
1246 nigel 63 </P>
1247     <P>
1248     A pattern is automatically anchored by PCRE if all of its top-level
1249     alternatives begin with one of the following:
1250     <pre>
1251     ^ unless PCRE_MULTILINE is set
1252     \A always
1253     \G always
1254 nigel 75 .* if PCRE_DOTALL is set and there are no back references to the subpattern in which .* appears
1255     </pre>
1256 nigel 63 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
1257     <b>pcre_fullinfo()</b>.
1258     <pre>
1260 nigel 75 </pre>
1261 ph10 784 Return the size of the compiled pattern. The fourth argument should point to a
1262     <b>size_t</b> variable. This value does not include the size of the <b>pcre</b>
1263     structure that is returned by <b>pcre_compile()</b>. The value that is passed as
1264     the argument to <b>pcre_malloc()</b> when <b>pcre_compile()</b> is getting memory
1265     in which to place the compiled data is the value returned by this option plus
1266     the size of the <b>pcre</b> structure. Studying a compiled pattern, with or
1267     without JIT, does not alter the value returned by this option.
1268 nigel 63 <pre>
1270 nigel 75 </pre>
1271 ph10 656 Return the size of the data block pointed to by the <i>study_data</i> field in a
1272     <b>pcre_extra</b> block. If <b>pcre_extra</b> is NULL, or there is no study data,
1273     zero is returned. The fourth argument should point to a <b>size_t</b> variable.
1274     The <i>study_data</i> field is set by <b>pcre_study()</b> to record information
1275     that will speed up matching (see the section entitled
1276     <a href="#studyingapattern">"Studying a pattern"</a>
1277     above). The format of the <i>study_data</i> block is private, but its length
1278     is made available via this option so that it can be saved and restored (see the
1279     <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1280     documentation for details).
1281 nigel 63 </P>
1282 ph10 691 <br><a name="SEC14" href="#TOC1">OBSOLETE INFO FUNCTION</a><br>
1283 nigel 63 <P>
1284     <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
1285     <b>*<i>firstcharptr</i>);</b>
1286     </P>
1287     <P>
1288     The <b>pcre_info()</b> function is now obsolete because its interface is too
1289     restrictive to return all the available data about a compiled pattern. New
1290     programs should use <b>pcre_fullinfo()</b> instead. The yield of
1291     <b>pcre_info()</b> is the number of capturing subpatterns, or one of the
1292     following negative numbers:
1293     <pre>
1294     PCRE_ERROR_NULL the argument <i>code</i> was NULL
1295     PCRE_ERROR_BADMAGIC the "magic number" was not found
1296 nigel 75 </pre>
1297 nigel 63 If the <i>optptr</i> argument is not NULL, a copy of the options with which the
1298     pattern was compiled is placed in the integer it points to (see
1299     PCRE_INFO_OPTIONS above).
1300     </P>
1301     <P>
1302     If the pattern is not anchored and the <i>firstcharptr</i> argument is not NULL,
1303     it is used to pass back information about the first character of any matched
1304     string (see PCRE_INFO_FIRSTBYTE above).
1305     </P>
1306 ph10 691 <br><a name="SEC15" href="#TOC1">REFERENCE COUNTS</a><br>
1307 nigel 63 <P>
1308 nigel 77 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
1309     </P>
1310     <P>
1311     The <b>pcre_refcount()</b> function is used to maintain a reference count in the
1312     data block that contains a compiled pattern. It is provided for the benefit of
1313     applications that operate in an object-oriented manner, where different parts
1314     of the application may be using the same compiled pattern, but you want to free
1315     the block when they are all done.
1316     </P>
1317     <P>
1318     When a pattern is compiled, the reference count field is initialized to zero.
1319     It is changed only by calling this function, whose action is to add the
1320     <i>adjust</i> value (which may be positive or negative) to it. The yield of the
1321     function is the new value. However, the value of the count is constrained to
1322     lie between 0 and 65535, inclusive. If the new value is outside these limits,
1323     it is forced to the appropriate limit value.
1324     </P>
1325     <P>
1326     Except when it is zero, the reference count is not correctly preserved if a
1327     pattern is compiled on one host and then transferred to a host whose byte-order
1328     is different. (This seems a highly unlikely scenario.)
1329     </P>
1330 ph10 691 <br><a name="SEC16" href="#TOC1">MATCHING A PATTERN: THE TRADITIONAL FUNCTION</a><br>
1331 nigel 77 <P>
1332 nigel 63 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1333     <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1334     <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
1335     </P>
1336     <P>
1337     The function <b>pcre_exec()</b> is called to match a subject string against a
1338 nigel 75 compiled pattern, which is passed in the <i>code</i> argument. If the
1339 ph10 461 pattern was studied, the result of the study should be passed in the
1340 ph10 708 <i>extra</i> argument. You can call <b>pcre_exec()</b> with the same <i>code</i>
1341     and <i>extra</i> arguments as many times as you like, in order to match
1342     different subject strings with the same pattern.
1343     </P>
1344     <P>
1345     This function is the main matching facility of the library, and it operates in
1346     a Perl-like manner. For specialist use there is also an alternative matching
1347     function, which is described
1348 nigel 77 <a href="#dfamatch">below</a>
1349     in the section about the <b>pcre_dfa_exec()</b> function.
1350 nigel 63 </P>
1351     <P>
1352 nigel 75 In most applications, the pattern will have been compiled (and optionally
1353     studied) in the same process that calls <b>pcre_exec()</b>. However, it is
1354     possible to save compiled patterns and study data, and then use them later
1355     in different processes, possibly even on different hosts. For a discussion
1356     about this, see the
1357     <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1358     documentation.
1359 nigel 63 </P>
1360     <P>
1361 nigel 75 Here is an example of a simple call to <b>pcre_exec()</b>:
1362 nigel 63 <pre>
1363     int rc;
1364     int ovector[30];
1365     rc = pcre_exec(
1366     re, /* result of pcre_compile() */
1367     NULL, /* we didn't study the pattern */
1368     "some string", /* the subject string */
1369     11, /* the length of the subject string */
1370     0, /* start at offset 0 in the subject */
1371     0, /* default options */
1372 nigel 75 ovector, /* vector of integers for substring information */
1373 nigel 77 30); /* number of elements (NOT size in bytes) */
1374 nigel 75 <a name="extradata"></a></PRE>
1375 nigel 63 </P>
1376 nigel 75 <br><b>
1377     Extra data for <b>pcre_exec()</b>
1378     </b><br>
1379 nigel 63 <P>
1380     If the <i>extra</i> argument is not NULL, it must point to a <b>pcre_extra</b>
1381     data block. The <b>pcre_study()</b> function returns such a block (when it
1382     doesn't return NULL), but you can also create one for yourself, and pass
1383 nigel 87 additional information in it. The <b>pcre_extra</b> block contains the following
1384     fields (not necessarily in this order):
1385 nigel 63 <pre>
1386     unsigned long int <i>flags</i>;
1387     void *<i>study_data</i>;
1388 ph10 691 void *<i>executable_jit</i>;
1389 nigel 63 unsigned long int <i>match_limit</i>;
1390 nigel 87 unsigned long int <i>match_limit_recursion</i>;
1391 nigel 63 void *<i>callout_data</i>;
1392 nigel 75 const unsigned char *<i>tables</i>;
1393 ph10 512 unsigned char **<i>mark</i>;
1394 nigel 75 </pre>
1395 nigel 63 The <i>flags</i> field is a bitmap that specifies which of the other fields
1396     are set. The flag bits are:
1397     <pre>
1403 nigel 75 PCRE_EXTRA_TABLES
1404 ph10 512 PCRE_EXTRA_MARK
1405 nigel 75 </pre>
1406 ph10 691 Other flag bits should be set to zero. The <i>study_data</i> field and sometimes
1407     the <i>executable_jit</i> field are set in the <b>pcre_extra</b> block that is
1408     returned by <b>pcre_study()</b>, together with the appropriate flag bits. You
1409     should not set these yourself, but you may add to the block by setting the
1410     other fields and their corresponding flag bits.
1411 nigel 63 </P>
1412     <P>
1413     The <i>match_limit</i> field provides a means of preventing PCRE from using up a
1414     vast amount of resources when running patterns that are not going to match,
1415     but which have a very large number of possibilities in their search trees. The
1416 ph10 461 classic example is a pattern that uses nested unlimited repeats.
1417 nigel 63 </P>
1418     <P>
1419 ph10 691 Internally, <b>pcre_exec()</b> uses a function called <b>match()</b>, which it
1420     calls repeatedly (sometimes recursively). The limit set by <i>match_limit</i> is
1421     imposed on the number of times this function is called during a match, which
1422     has the effect of limiting the amount of backtracking that can take place. For
1423     patterns that are not anchored, the count restarts from zero for each position
1424     in the subject string.
1425 nigel 75 </P>
1426     <P>
1427 ph10 691 When <b>pcre_exec()</b> is called with a pattern that was successfully studied
1428     with the PCRE_STUDY_JIT_COMPILE option, the way that the matching is executed
1429     is entirely different. However, there is still the possibility of runaway
1430     matching that goes on for a very long time, and so the <i>match_limit</i> value
1431     is also used in this case (but in a different way) to limit how long the
1432     matching can continue.
1433     </P>
1434     <P>
1435 nigel 87 The default value for the limit can be set when PCRE is built; the default
1436 nigel 63 default is 10 million, which handles all but the most extreme cases. You can
1437 nigel 87 override the default by suppling <b>pcre_exec()</b> with a <b>pcre_extra</b>
1438     block in which <i>match_limit</i> is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1439     the <i>flags</i> field. If the limit is exceeded, <b>pcre_exec()</b> returns
1441 nigel 63 </P>
1442     <P>
1443 nigel 87 The <i>match_limit_recursion</i> field is similar to <i>match_limit</i>, but
1444     instead of limiting the total number of times that <b>match()</b> is called, it
1445     limits the depth of recursion. The recursion depth is a smaller number than the
1446     total number of calls, because not all calls to <b>match()</b> are recursive.
1447     This limit is of use only if it is set smaller than <i>match_limit</i>.
1448     </P>
1449     <P>
1450 ph10 691 Limiting the recursion depth limits the amount of machine stack that can be
1451     used, or, when PCRE has been compiled to use memory on the heap instead of the
1452     stack, the amount of heap memory that can be used. This limit is not relevant,
1453     and is ignored, if the pattern was successfully studied with
1455 nigel 87 </P>
1456     <P>
1457     The default value for <i>match_limit_recursion</i> can be set when PCRE is
1458     built; the default default is the same value as the default for
1459     <i>match_limit</i>. You can override the default by suppling <b>pcre_exec()</b>
1460     with a <b>pcre_extra</b> block in which <i>match_limit_recursion</i> is set, and
1461     PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the <i>flags</i> field. If the limit
1462     is exceeded, <b>pcre_exec()</b> returns PCRE_ERROR_RECURSIONLIMIT.
1463     </P>
1464     <P>
1465 ph10 453 The <i>callout_data</i> field is used in conjunction with the "callout" feature,
1466     and is described in the
1467 nigel 75 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1468     documentation.
1469 nigel 63 </P>
1470     <P>
1471 nigel 75 The <i>tables</i> field is used to pass a character tables pointer to
1472     <b>pcre_exec()</b>; this overrides the value that is stored with the compiled
1473     pattern. A non-NULL value is stored with the compiled pattern only if custom
1474     tables were supplied to <b>pcre_compile()</b> via its <i>tableptr</i> argument.
1475     If NULL is passed to <b>pcre_exec()</b> using this mechanism, it forces PCRE's
1476     internal tables to be used. This facility is helpful when re-using patterns
1477     that have been saved after compiling with an external set of tables, because
1478     the external tables might be at a different address when <b>pcre_exec()</b> is
1479     called. See the
1480     <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1481     documentation for a discussion of saving compiled patterns for later use.
1482 ph10 512 </P>
1483     <P>
1484     If PCRE_EXTRA_MARK is set in the <i>flags</i> field, the <i>mark</i> field must
1485     be set to point to a <b>char *</b> variable. If the pattern contains any
1486     backtracking control verbs such as (*MARK:NAME), and the execution ends up with
1487     a name to pass back, a pointer to the name string (zero terminated) is placed
1488     in the variable pointed to by the <i>mark</i> field. The names are within the
1489     compiled pattern; if you wish to retain such a name you must copy it before
1490     freeing the memory of a compiled pattern. If there is no name to pass back, the
1491     variable pointed to by the <i>mark</i> field set to NULL. For details of the
1492     backtracking control verbs, see the section entitled
1493     <a href="pcrepattern#backtrackcontrol">"Backtracking control"</a>
1494     in the
1495     <a href="pcrepattern.html"><b>pcrepattern</b></a>
1496     documentation.
1497 ph10 227 <a name="execoptions"></a></P>
1498 nigel 75 <br><b>
1499     Option bits for <b>pcre_exec()</b>
1500     </b><br>
1501 nigel 63 <P>
1502 nigel 75 The unused bits of the <i>options</i> argument for <b>pcre_exec()</b> must be
1503 nigel 91 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1507 ph10 691 </P>
1508     <P>
1509     If the pattern was successfully studied with the PCRE_STUDY_JIT_COMPILE option,
1510     the only supported options for JIT execution are PCRE_NO_UTF8_CHECK,
1512     particular that partial matching is not supported. If an unsupported option is
1513     used, JIT execution is disabled and the normal interpretive code in
1514     <b>pcre_exec()</b> is run.
1515 nigel 63 <pre>
1516 nigel 75 PCRE_ANCHORED
1517     </pre>
1518     The PCRE_ANCHORED option limits <b>pcre_exec()</b> to matching at the first
1519     matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1520     to be anchored by virtue of its contents, it cannot be made unachored at
1521     matching time.
1522     <pre>
1523 ph10 231 PCRE_BSR_ANYCRLF
1525     </pre>
1526     These options (which are mutually exclusive) control what the \R escape
1527     sequence matches. The choice is either to match only CR, LF, or CRLF, or to
1528     match any Unicode newline sequence. These options override the choice that was
1529     made or defaulted when the pattern was compiled.
1530     <pre>
1531 nigel 91 PCRE_NEWLINE_CR
1535 nigel 93 PCRE_NEWLINE_ANY
1536 nigel 91 </pre>
1537     These options override the newline definition that was chosen or defaulted when
1538 nigel 93 the pattern was compiled. For details, see the description of
1539     <b>pcre_compile()</b> above. During matching, the newline choice affects the
1540     behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1541     the way the match position is advanced after a match failure for an unanchored
1542 ph10 227 pattern.
1543     </P>
1544     <P>
1546     match attempt for an unanchored pattern fails when the current position is at a
1547 ph10 231 CRLF sequence, and the pattern contains no explicit matches for CR or LF
1548 ph10 227 characters, the match position is advanced by two characters instead of one, in
1549     other words, to after the CRLF.
1550     </P>
1551     <P>
1552     The above rule is a compromise that makes the most common cases work as
1553     expected. For example, if the pattern is .+A (and the PCRE_DOTALL option is not
1554     set), it does not match the string "\r\nA" because, after failing at the
1555     start, it skips both the CR and the LF before retrying. However, the pattern
1556     [\r\n]A does match that string, because it contains an explicit CR or LF
1557     reference, and so advances only by one character after the first failure.
1558     </P>
1559     <P>
1560 ph10 231 An explicit match for CR of LF is either a literal appearance of one of those
1561     characters, or one of the \r or \n escape sequences. Implicit matches such as
1562     [^X] do not count, nor does \s (which includes CR and LF in the characters
1563     that it matches).
1564     </P>
1565     <P>
1566 ph10 227 Notwithstanding the above, anomalous effects may still occur when CRLF is a
1567     valid newline sequence and explicit \r or \n escapes appear in the pattern.
1568 nigel 91 <pre>
1569 nigel 63 PCRE_NOTBOL
1570 nigel 75 </pre>
1571     This option specifies that first character of the subject string is not the
1572     beginning of a line, so the circumflex metacharacter should not match before
1573     it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1574     never to match. This option affects only the behaviour of the circumflex
1575     metacharacter. It does not affect \A.
1576 nigel 63 <pre>
1577     PCRE_NOTEOL
1578 nigel 75 </pre>
1579     This option specifies that the end of the subject string is not the end of a
1580     line, so the dollar metacharacter should not match it nor (except in multiline
1581     mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1582     compile time) causes dollar never to match. This option affects only the
1583     behaviour of the dollar metacharacter. It does not affect \Z or \z.
1584 nigel 63 <pre>
1586 nigel 75 </pre>
1587 nigel 63 An empty string is not considered to be a valid match if this option is set. If
1588     there are alternatives in the pattern, they are tried. If all the alternatives
1589     match the empty string, the entire match fails. For example, if the pattern
1590     <pre>
1591     a?b?
1592 nigel 75 </pre>
1593 ph10 453 is applied to a string not beginning with "a" or "b", it matches an empty
1594 nigel 63 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1595     valid, so PCRE searches further into the string for occurrences of "a" or "b".
1596 ph10 453 <pre>
1598     </pre>
1599 ph10 461 This is like PCRE_NOTEMPTY, except that an empty string match that is not at
1600 ph10 453 the start of the subject is permitted. If the pattern is anchored, such a match
1601     can occur only if the pattern contains \K.
1602 nigel 63 </P>
1603     <P>
1604 ph10 453 Perl has no direct equivalent of PCRE_NOTEMPTY or PCRE_NOTEMPTY_ATSTART, but it
1605     does make a special case of a pattern match of the empty string within its
1606     <b>split()</b> function, and when using the /g modifier. It is possible to
1607     emulate Perl's behaviour after matching a null string by first trying the match
1608     again at the same offset with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then
1609     if that fails, by advancing the starting offset (see below) and trying an
1610     ordinary match again. There is some code that demonstrates how to do this in
1611     the
1612 ph10 429 <a href="pcredemo.html"><b>pcredemo</b></a>
1613 ph10 572 sample program. In the most general case, you have to check to see if the
1614     newline convention recognizes CRLF as a newline, and if so, and the current
1615 ph10 567 character is CR followed by LF, advance the starting offset by two characters
1616     instead of one.
1617 nigel 75 <pre>
1619     </pre>
1620     There are a number of optimizations that <b>pcre_exec()</b> uses at the start of
1621 ph10 545 a match, in order to speed up the process. For example, if it is known that an
1622     unanchored match must start with a specific character, it searches the subject
1623     for that character, and fails immediately if it cannot find it, without
1624     actually running the main matching function. This means that a special item
1625     such as (*COMMIT) at the start of a pattern is not considered until after a
1626 ph10 548 suitable starting point for the match has been found. When callouts or (*MARK)
1627     items are in use, these "start-up" optimizations can cause them to be skipped
1628     if the pattern is never actually used. The start-up optimizations are in effect
1629     a pre-scan of the subject that takes place before the pattern is run.
1630     </P>
1631     <P>
1632     The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations, possibly
1633     causing performance to suffer, but ensuring that in cases where the result is
1634     "no match", the callouts do occur, and that items such as (*COMMIT) and (*MARK)
1635 ph10 579 are considered at every possible starting position in the subject string. If
1636     PCRE_NO_START_OPTIMIZE is set at compile time, it cannot be unset at matching
1637     time.
1638     </P>
1639     <P>
1640 ph10 548 Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching operation.
1641     Consider the pattern
1642 ph10 392 <pre>
1643 ph10 548 (*COMMIT)ABC
1644     </pre>
1645     When this is compiled, PCRE records the fact that a match must start with the
1646     character "A". Suppose the subject string is "DEFABC". The start-up
1647     optimization scans along the subject, finds "A" and runs the first match
1648     attempt from there. The (*COMMIT) item means that the pattern must match the
1649     current starting position, which in this case, it does. However, if the same
1650     match is run with PCRE_NO_START_OPTIMIZE set, the initial scan along the
1651     subject string does not happen. The first match attempt is run starting from
1652     "D" and when this fails, (*COMMIT) prevents any further matches being tried, so
1653     the overall result is "no match". If the pattern is studied, more start-up
1654     optimizations may be used. For example, a minimum length for the subject may be
1655     recorded. Consider the pattern
1656     <pre>
1657     (*MARK:A)(X|Y)
1658     </pre>
1659     The minimum length for a match is one character. If the subject is "ABC", there
1660     will be attempts to match "ABC", "BC", "C", and then finally an empty string.
1661     If the pattern is studied, the final attempt does not take place, because PCRE
1662     knows that the subject is too short, and so the (*MARK) is never encountered.
1663     In this case, studying the pattern does not affect the overall match result,
1664     which is still "no match", but it does affect the auxiliary information that is
1665     returned.
1666     <pre>
1667 nigel 75 PCRE_NO_UTF8_CHECK
1668     </pre>
1669     When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1670     string is automatically checked when <b>pcre_exec()</b> is subsequently called.
1671     The value of <i>startoffset</i> is also checked to ensure that it points to the
1672 ph10 211 start of a UTF-8 character. There is a discussion about the validity of UTF-8
1673     strings in the
1674     <a href="pcre.html#utf8strings">section on UTF-8 support</a>
1675     in the main
1676     <a href="pcre.html"><b>pcre</b></a>
1677     page. If an invalid UTF-8 sequence of bytes is found, <b>pcre_exec()</b> returns
1678 ph10 572 the error PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is
1679 ph10 654 a truncated UTF-8 character at the end of the subject, PCRE_ERROR_SHORTUTF8. In
1680     both cases, information about the precise nature of the error may also be
1681     returned (see the descriptions of these errors in the section entitled \fIError
1682     return values from\fP <b>pcre_exec()</b>
1683     <a href="#errorlist">below).</a>
1684     If <i>startoffset</i> contains a value that does not point to the start of a
1685     UTF-8 character (or to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is
1686 ph10 572 returned.
1687 nigel 63 </P>
1688     <P>
1689 nigel 75 If you already know that your subject is valid, and you want to skip these
1690     checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1691     calling <b>pcre_exec()</b>. You might want to do this for the second and
1692     subsequent calls to <b>pcre_exec()</b> if you are making repeated calls to find
1693     all the matches in a single subject string. However, you should be sure that
1694 ph10 567 the value of <i>startoffset</i> points to the start of a UTF-8 character (or the
1695     end of the subject). When PCRE_NO_UTF8_CHECK is set, the effect of passing an
1696     invalid UTF-8 string as a subject or an invalid value of <i>startoffset</i> is
1697     undefined. Your program may crash.
1698 nigel 75 <pre>
1699 ph10 461 PCRE_PARTIAL_HARD
1700 ph10 429 PCRE_PARTIAL_SOFT
1701 nigel 75 </pre>
1702 ph10 429 These options turn on the partial matching feature. For backwards
1703     compatibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial match
1704     occurs if the end of the subject string is reached successfully, but there are
1705     not enough subject characters to complete the match. If this happens when
1706 ph10 567 PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set, matching continues by
1707     testing any remaining alternatives. Only if no complete match can be found is
1708     PCRE_ERROR_PARTIAL returned instead of PCRE_ERROR_NOMATCH. In other words,
1709     PCRE_PARTIAL_SOFT says that the caller is prepared to handle a partial match,
1710     but only if no complete match can be found.
1711     </P>
1712     <P>
1713     If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this case, if a
1714     partial match is found, <b>pcre_exec()</b> immediately returns
1715     PCRE_ERROR_PARTIAL, without considering any other alternatives. In other words,
1716 ph10 572 when PCRE_PARTIAL_HARD is set, a partial match is considered to be more
1717 ph10 567 important that an alternative complete match.
1718     </P>
1719     <P>
1720     In both cases, the portion of the string that was inspected when the partial
1721     match was found is set as the first matching string. There is a more detailed
1722     discussion of partial and multi-segment matching, with examples, in the
1723 nigel 75 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1724     documentation.
1725     </P>
1726     <br><b>
1727     The string to be matched by <b>pcre_exec()</b>
1728     </b><br>
1729     <P>
1730 nigel 63 The subject string is passed to <b>pcre_exec()</b> as a pointer in
1731 ph10 371 <i>subject</i>, a length (in bytes) in <i>length</i>, and a starting byte offset
1732 ph10 572 in <i>startoffset</i>. If this is negative or greater than the length of the
1733     subject, <b>pcre_exec()</b> returns PCRE_ERROR_BADOFFSET. When the starting
1734     offset is zero, the search for a match starts at the beginning of the subject,
1735     and this is by far the most common case. In UTF-8 mode, the byte offset must
1736     point to the start of a UTF-8 character (or the end of the subject). Unlike the
1737     pattern string, the subject may contain binary zero bytes.
1738 nigel 63 </P>
1739     <P>
1740     A non-zero starting offset is useful when searching for another match in the
1741     same subject by calling <b>pcre_exec()</b> again after a previous success.
1742     Setting <i>startoffset</i> differs from just passing over a shortened string and
1743     setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1744     lookbehind. For example, consider the pattern
1745     <pre>
1746     \Biss\B
1747 nigel 75 </pre>
1748 nigel 63 which finds occurrences of "iss" in the middle of words. (\B matches only if
1749     the current position in the subject is not a word boundary.) When applied to
1750     the string "Mississipi" the first call to <b>pcre_exec()</b> finds the first
1751     occurrence. If <b>pcre_exec()</b> is called again with just the remainder of the
1752     subject, namely "issipi", it does not match, because \B is always false at the
1753     start of the subject, which is deemed to be a word boundary. However, if
1754     <b>pcre_exec()</b> is passed the entire string again, but with <i>startoffset</i>
1755     set to 4, it finds the second occurrence of "iss" because it is able to look
1756     behind the starting point to discover that it is preceded by a letter.
1757     </P>
1758     <P>
1759 ph10 567 Finding all the matches in a subject is tricky when the pattern can match an
1760     empty string. It is possible to emulate Perl's /g behaviour by first trying the
1761     match again at the same offset, with the PCRE_NOTEMPTY_ATSTART and
1762     PCRE_ANCHORED options, and then if that fails, advancing the starting offset
1763     and trying an ordinary match again. There is some code that demonstrates how to
1764     do this in the
1765     <a href="pcredemo.html"><b>pcredemo</b></a>
1766 ph10 572 sample program. In the most general case, you have to check to see if the
1767     newline convention recognizes CRLF as a newline, and if so, and the current
1768 ph10 567 character is CR followed by LF, advance the starting offset by two characters
1769     instead of one.
1770     </P>
1771     <P>
1772 nigel 63 If a non-zero starting offset is passed when the pattern is anchored, one
1773 nigel 75 attempt to match at the given offset is made. This can only succeed if the
1774 nigel 63 pattern does not require the match to be at the start of the subject.
1775     </P>
1776 nigel 75 <br><b>
1777     How <b>pcre_exec()</b> returns captured substrings
1778     </b><br>
1779 nigel 63 <P>
1780     In general, a pattern matches a certain portion of the subject, and in
1781     addition, further substrings from the subject may be picked out by parts of the
1782     pattern. Following the usage in Jeffrey Friedl's book, this is called
1783     "capturing" in what follows, and the phrase "capturing subpattern" is used for
1784     a fragment of a pattern that picks out a substring. PCRE supports several other
1785     kinds of parenthesized subpattern that do not cause substrings to be captured.
1786     </P>
1787     <P>
1788 ph10 371 Captured substrings are returned to the caller via a vector of integers whose
1789     address is passed in <i>ovector</i>. The number of elements in the vector is
1790     passed in <i>ovecsize</i>, which must be a non-negative number. <b>Note</b>: this
1791     argument is NOT the size of <i>ovector</i> in bytes.
1792 nigel 63 </P>
1793     <P>
1794 nigel 75 The first two-thirds of the vector is used to pass back captured substrings,
1795     each substring using a pair of integers. The remaining third of the vector is
1796     used as workspace by <b>pcre_exec()</b> while matching capturing subpatterns,
1797 ph10 371 and is not available for passing back information. The number passed in
1798 nigel 75 <i>ovecsize</i> should always be a multiple of three. If it is not, it is
1799     rounded down.
1800     </P>
1801     <P>
1802     When a match is successful, information about captured substrings is returned
1803     in pairs of integers, starting at the beginning of <i>ovector</i>, and
1804 ph10 371 continuing up to two-thirds of its length at the most. The first element of
1805     each pair is set to the byte offset of the first character in a substring, and
1806     the second is set to the byte offset of the first character after the end of a
1807     substring. <b>Note</b>: these values are always byte offsets, even in UTF-8
1808     mode. They are not character counts.
1809 nigel 63 </P>
1810     <P>
1811 ph10 371 The first pair of integers, <i>ovector[0]</i> and <i>ovector[1]</i>, identify the
1812     portion of the subject string matched by the entire pattern. The next pair is
1813     used for the first capturing subpattern, and so on. The value returned by
1814     <b>pcre_exec()</b> is one more than the highest numbered pair that has been set.
1815     For example, if two substrings have been captured, the returned value is 3. If
1816     there are no capturing subpatterns, the return value from a successful match is
1817     1, indicating that just the first pair of offsets has been set.
1818     </P>
1819     <P>
1820 nigel 63 If a capturing subpattern is matched repeatedly, it is the last portion of the
1821 nigel 75 string that it matched that is returned.
1822 nigel 63 </P>
1823     <P>
1824 nigel 75 If the vector is too small to hold all the captured substring offsets, it is
1825     used as far as possible (up to two-thirds of its length), and the function
1826 ph10 691 returns a value of zero. If neither the actual string matched not any captured
1827     substrings are of interest, <b>pcre_exec()</b> may be called with <i>ovector</i>
1828     passed as NULL and <i>ovecsize</i> as zero. However, if the pattern contains
1829     back references and the <i>ovector</i> is not big enough to remember the related
1830     substrings, PCRE has to get additional memory for use during matching. Thus it
1831     is usually advisable to supply an <i>ovector</i> of reasonable size.
1832 nigel 63 </P>
1833     <P>
1834 ph10 691 There are some cases where zero is returned (indicating vector overflow) when
1835     in fact the vector is exactly the right size for the final match. For example,
1836     consider the pattern
1837     <pre>
1838     (a)(?:(b)c|bd)
1839     </pre>
1840     If a vector of 6 elements (allowing for only 1 captured substring) is given
1841     with subject string "abd", <b>pcre_exec()</b> will try to set the second
1842     captured string, thereby recording a vector overflow, before failing to match
1843     "c" and backing up to try the second alternative. The zero return, however,
1844     does correctly indicate that the maximum number of slots (namely 2) have been
1845     filled. In similar cases where there is temporary overflow, but the final
1846     number of used slots is actually less than the maximum, a non-zero value is
1847     returned.
1848     </P>
1849     <P>
1850 ph10 461 The <b>pcre_fullinfo()</b> function can be used to find out how many capturing
1851 nigel 63 subpatterns there are in a compiled pattern. The smallest size for
1852     <i>ovector</i> that will allow for <i>n</i> captured substrings, in addition to
1853     the offsets of the substring matched by the whole pattern, is (<i>n</i>+1)*3.
1854 nigel 91 </P>
1855     <P>
1856     It is possible for capturing subpattern number <i>n+1</i> to match some part of
1857     the subject when subpattern <i>n</i> has not been used at all. For example, if
1858     the string "abc" is matched against the pattern (a|(z))(bc) the return from the
1859     function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
1860     happens, both values in the offset pairs corresponding to unused subpatterns
1861     are set to -1.
1862     </P>
1863     <P>
1864     Offset values that correspond to unused subpatterns at the end of the
1865     expression are also set to -1. For example, if the string "abc" is matched
1866     against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1867     return from the function is 2, because the highest used capturing subpattern
1868 ph10 572 number is 1, and the offsets for for the second and third capturing subpatterns
1869     (assuming the vector is large enough, of course) are set to -1.
1870 nigel 91 </P>
1871     <P>
1872 ph10 691 <b>Note</b>: Elements in the first two-thirds of <i>ovector</i> that do not
1873     correspond to capturing parentheses in the pattern are never changed. That is,
1874     if a pattern contains <i>n</i> capturing parentheses, no more than
1875     <i>ovector[0]</i> to <i>ovector[2n+1]</i> are set by <b>pcre_exec()</b>. The other
1876     elements (in the first two-thirds) retain whatever values they previously had.
1877 ph10 572 </P>
1878     <P>
1879 nigel 91 Some convenience functions are provided for extracting the captured substrings
1880     as separate strings. These are described below.
1881 nigel 77 <a name="errorlist"></a></P>
1882 nigel 75 <br><b>
1883 nigel 91 Error return values from <b>pcre_exec()</b>
1884 nigel 75 </b><br>
1885 nigel 63 <P>
1886     If <b>pcre_exec()</b> fails, it returns a negative number. The following are
1887     defined in the header file:
1888     <pre>
1889     PCRE_ERROR_NOMATCH (-1)
1890 nigel 75 </pre>
1891 nigel 63 The subject string did not match the pattern.
1892     <pre>
1893     PCRE_ERROR_NULL (-2)
1894 nigel 75 </pre>
1895 nigel 63 Either <i>code</i> or <i>subject</i> was passed as NULL, or <i>ovector</i> was
1896     NULL and <i>ovecsize</i> was not zero.
1897     <pre>
1899 nigel 75 </pre>
1900 nigel 63 An unrecognized bit was set in the <i>options</i> argument.
1901     <pre>
1903 nigel 75 </pre>
1904 nigel 63 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1905 nigel 75 the case when it is passed a junk pointer and to detect when a pattern that was
1906     compiled in an environment of one endianness is run in an environment with the
1907     other endianness. This is the error that PCRE gives when the magic number is
1908     not present.
1909 nigel 63 <pre>
1910 nigel 93 PCRE_ERROR_UNKNOWN_OPCODE (-5)
1911 nigel 75 </pre>
1912 nigel 63 While running the pattern match, an unknown item was encountered in the
1913     compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1914     of the compiled pattern.
1915     <pre>
1917 nigel 75 </pre>
1918 nigel 63 If a pattern contains back references, but the <i>ovector</i> that is passed to
1919     <b>pcre_exec()</b> is not big enough to remember the referenced substrings, PCRE
1920     gets a block of memory at the start of matching to use for this purpose. If the
1921 nigel 75 call via <b>pcre_malloc()</b> fails, this error is given. The memory is
1922     automatically freed at the end of matching.
1923 ph10 535 </P>
1924     <P>
1925     This error is also given if <b>pcre_stack_malloc()</b> fails in
1926     <b>pcre_exec()</b>. This can happen only when PCRE has been compiled with
1927     <b>--disable-stack-for-recursion</b>.
1928 nigel 63 <pre>
1930 nigel 75 </pre>
1931 nigel 63 This error is used by the <b>pcre_copy_substring()</b>,
1932     <b>pcre_get_substring()</b>, and <b>pcre_get_substring_list()</b> functions (see
1933     below). It is never returned by <b>pcre_exec()</b>.
1934     <pre>
1936 nigel 75 </pre>
1937 nigel 87 The backtracking limit, as specified by the <i>match_limit</i> field in a
1938     <b>pcre_extra</b> structure (or defaulted) was reached. See the description
1939     above.
1940     <pre>
1941 nigel 63 PCRE_ERROR_CALLOUT (-9)
1942 nigel 75 </pre>
1943 nigel 63 This error is never generated by <b>pcre_exec()</b> itself. It is provided for
1944     use by callout functions that want to yield a distinctive error code. See the
1945 nigel 75 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1946     documentation for details.
1947 nigel 71 <pre>
1948 nigel 73 PCRE_ERROR_BADUTF8 (-10)
1949 nigel 75 </pre>
1950 ph10 654 A string that contains an invalid UTF-8 byte sequence was passed as a subject,
1951     and the PCRE_NO_UTF8_CHECK option was not set. If the size of the output vector
1952     (<i>ovecsize</i>) is at least 2, the byte offset to the start of the the invalid
1953     UTF-8 character is placed in the first element, and a reason code is placed in
1954     the second element. The reason codes are listed in the
1955     <a href="#badutf8reasons">following section.</a>
1956     For backward compatibility, if PCRE_PARTIAL_HARD is set and the problem is a
1957     truncated UTF-8 character at the end of the subject (reason codes 1 to 5),
1958     PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8.
1959 nigel 73 <pre>
1961 nigel 75 </pre>
1962 ph10 654 The UTF-8 byte sequence that was passed as a subject was checked and found to
1963     be valid (the PCRE_NO_UTF8_CHECK option was not set), but the value of
1964     <i>startoffset</i> did not point to the beginning of a UTF-8 character or the
1965 ph10 572 end of the subject.
1966 nigel 75 <pre>
1967 nigel 77 PCRE_ERROR_PARTIAL (-12)
1968 nigel 75 </pre>
1969     The subject string did not match, but it did match partially. See the
1970     <a href="pcrepartial.html"><b>pcrepartial</b></a>
1971     documentation for details of partial matching.
1972     <pre>
1973 nigel 77 PCRE_ERROR_BADPARTIAL (-13)
1974 nigel 75 </pre>
1975 ph10 429 This code is no longer in use. It was formerly returned when the PCRE_PARTIAL
1976     option was used with a compiled pattern containing items that were not
1977 ph10 461 supported for partial matching. From release 8.00 onwards, there are no
1978 ph10 429 restrictions on partial matching.
1979 nigel 75 <pre>
1980 nigel 77 PCRE_ERROR_INTERNAL (-14)
1981 nigel 75 </pre>
1982     An unexpected internal error has occurred. This error could be caused by a bug
1983     in PCRE or by overwriting of the compiled pattern.
1984     <pre>
1985 nigel 77 PCRE_ERROR_BADCOUNT (-15)
1986 nigel 75 </pre>
1987     This error is given if the value of the <i>ovecsize</i> argument is negative.
1988 nigel 93 <pre>
1990     </pre>
1991     The internal recursion limit, as specified by the <i>match_limit_recursion</i>
1992     field in a <b>pcre_extra</b> structure (or defaulted) was reached. See the
1993     description above.
1994     <pre>
1996     </pre>
1997     An invalid combination of PCRE_NEWLINE_<i>xxx</i> options was given.
1998 ph10 567 <pre>
2000     </pre>
2001 ph10 572 The value of <i>startoffset</i> was negative or greater than the length of the
2002 ph10 567 subject, that is, the value in <i>length</i>.
2003 ph10 572 <pre>
2004     PCRE_ERROR_SHORTUTF8 (-25)
2005     </pre>
2006 ph10 654 This error is returned instead of PCRE_ERROR_BADUTF8 when the subject string
2007     ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD option is set.
2008     Information about the failure is returned as for PCRE_ERROR_BADUTF8. It is in
2009     fact sufficient to detect this case, but this special error code for
2010     PCRE_PARTIAL_HARD precedes the implementation of returned information; it is
2011     retained for backwards compatibility.
2012     <pre>
2014     </pre>
2015     This error is returned when <b>pcre_exec()</b> detects a recursion loop within
2016     the pattern. Specifically, it means that either the whole pattern or a
2017     subpattern has been called recursively for the second time at the same position
2018     in the subject string. Some simple patterns that might do this are detected and
2019     faulted at compile time, but more complicated cases, in particular mutual
2020     recursions between two different subpatterns, cannot be detected until run
2021     time.
2022 ph10 691 <pre>
2024     </pre>
2025     This error is returned when a pattern that was successfully studied using the
2026     PCRE_STUDY_JIT_COMPILE option is being matched, but the memory available for
2027     the just-in-time processing stack is not large enough. See the
2028     <a href="pcrejit.html"><b>pcrejit</b></a>
2029     documentation for more details.
2030 nigel 73 </P>
2031 nigel 93 <P>
2032 ph10 197 Error numbers -16 to -20 and -22 are not used by <b>pcre_exec()</b>.
2033 ph10 654 <a name="badutf8reasons"></a></P>
2034     <br><b>
2035     Reason codes for invalid UTF-8 strings
2036     </b><br>
2037     <P>
2038     When <b>pcre_exec()</b> returns either PCRE_ERROR_BADUTF8 or
2039     PCRE_ERROR_SHORTUTF8, and the size of the output vector (<i>ovecsize</i>) is at
2040     least 2, the offset of the start of the invalid UTF-8 character is placed in
2041     the first output vector element (<i>ovector[0]</i>) and a reason code is placed
2042     in the second element (<i>ovector[1]</i>). The reason codes are given names in
2043     the <b>pcre.h</b> header file:
2044     <pre>
2045     PCRE_UTF8_ERR1
2046     PCRE_UTF8_ERR2
2047     PCRE_UTF8_ERR3
2048     PCRE_UTF8_ERR4
2049     PCRE_UTF8_ERR5
2050     </pre>
2051     The string ends with a truncated UTF-8 character; the code specifies how many
2052     bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8 characters to be
2053     no longer than 4 bytes, the encoding scheme (originally defined by RFC 2279)
2054     allows for up to 6 bytes, and this is checked first; hence the possibility of
2055     4 or 5 missing bytes.
2056     <pre>
2057     PCRE_UTF8_ERR6
2058     PCRE_UTF8_ERR7
2059     PCRE_UTF8_ERR8
2060     PCRE_UTF8_ERR9
2061     PCRE_UTF8_ERR10
2062     </pre>
2063     The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of the
2064     character do not have the binary value 0b10 (that is, either the most
2065     significant bit is 0, or the next bit is 1).
2066     <pre>
2067     PCRE_UTF8_ERR11
2068     PCRE_UTF8_ERR12
2069     </pre>
2070     A character that is valid by the RFC 2279 rules is either 5 or 6 bytes long;
2071     these code points are excluded by RFC 3629.
2072     <pre>
2073     PCRE_UTF8_ERR13
2074     </pre>
2075     A 4-byte character has a value greater than 0x10fff; these code points are
2076     excluded by RFC 3629.
2077     <pre>
2078     PCRE_UTF8_ERR14
2079     </pre>
2080     A 3-byte character has a value in the range 0xd800 to 0xdfff; this range of
2081     code points are reserved by RFC 3629 for use with UTF-16, and so are excluded
2082     from UTF-8.
2083     <pre>
2084     PCRE_UTF8_ERR15
2085     PCRE_UTF8_ERR16
2086     PCRE_UTF8_ERR17
2087     PCRE_UTF8_ERR18
2088     PCRE_UTF8_ERR19
2089     </pre>
2090     A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes for a
2091     value that can be represented by fewer bytes, which is invalid. For example,
2092     the two bytes 0xc0, 0xae give the value 0x2e, whose correct coding uses just
2093     one byte.
2094     <pre>
2095     PCRE_UTF8_ERR20
2096     </pre>
2097     The two most significant bits of the first byte of a character have the binary
2098     value 0b10 (that is, the most significant bit is 1 and the second is 0). Such a
2099     byte can only validly occur as the second or subsequent byte of a multi-byte
2100     character.
2101     <pre>
2102     PCRE_UTF8_ERR21
2103     </pre>
2104     The first byte of a character has the value 0xfe or 0xff. These values can
2105     never occur in a valid UTF-8 string.
2106 nigel 93 </P>
2107 ph10 691 <br><a name="SEC17" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a><br>
2108 nigel 63 <P>
2109     <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
2110     <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
2111     <b>int <i>buffersize</i>);</b>
2112     </P>
2113     <P>
2114     <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
2115     <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
2116     <b>const char **<i>stringptr</i>);</b>
2117     </P>
2118     <P>
2119     <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
2120     <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
2121     </P>
2122     <P>
2123     Captured substrings can be accessed directly by using the offsets returned by
2124     <b>pcre_exec()</b> in <i>ovector</i>. For convenience, the functions
2125     <b>pcre_copy_substring()</b>, <b>pcre_get_substring()</b>, and
2126     <b>pcre_get_substring_list()</b> are provided for extracting captured substrings
2127     as new, separate, zero-terminated strings. These functions identify substrings
2128     by number. The next section describes functions for extracting named
2129 nigel 91 substrings.
2130 nigel 63 </P>
2131     <P>
2132 nigel 91 A substring that contains a binary zero is correctly extracted and has a
2133     further zero added on the end, but the result is not, of course, a C string.
2134     However, you can process such a string by referring to the length that is
2135     returned by <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>.
2136     Unfortunately, the interface to <b>pcre_get_substring_list()</b> is not adequate
2137     for handling strings containing binary zeros, because the end of the final
2138     string is not independently indicated.
2139     </P>
2140     <P>
2141 nigel 63 The first three arguments are the same for all three of these functions:
2142 nigel 75 <i>subject</i> is the subject string that has just been successfully matched,
2143 nigel 63 <i>ovector</i> is a pointer to the vector of integer offsets that was passed to
2144     <b>pcre_exec()</b>, and <i>stringcount</i> is the number of substrings that were
2145     captured by the match, including the substring that matched the entire regular
2146 nigel 75 expression. This is the value returned by <b>pcre_exec()</b> if it is greater
2147     than zero. If <b>pcre_exec()</b> returned zero, indicating that it ran out of
2148     space in <i>ovector</i>, the value passed as <i>stringcount</i> should be the
2149     number of elements in the vector divided by three.
2150 nigel 63 </P>
2151     <P>
2152     The functions <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>
2153     extract a single substring, whose number is given as <i>stringnumber</i>. A
2154 nigel 75 value of zero extracts the substring that matched the entire pattern, whereas
2155 nigel 63 higher values extract the captured substrings. For <b>pcre_copy_substring()</b>,
2156     the string is placed in <i>buffer</i>, whose length is given by
2157     <i>buffersize</i>, while for <b>pcre_get_substring()</b> a new block of memory is
2158     obtained via <b>pcre_malloc</b>, and its address is returned via
2159     <i>stringptr</i>. The yield of the function is the length of the string, not
2160 nigel 93 including the terminating zero, or one of these error codes:
2161 nigel 63 <pre>
2163 nigel 75 </pre>
2164 nigel 63 The buffer was too small for <b>pcre_copy_substring()</b>, or the attempt to get
2165     memory failed for <b>pcre_get_substring()</b>.
2166     <pre>
2168 nigel 75 </pre>
2169 nigel 63 There is no substring whose number is <i>stringnumber</i>.
2170     </P>
2171     <P>
2172     The <b>pcre_get_substring_list()</b> function extracts all available substrings
2173     and builds a list of pointers to them. All this is done in a single block of
2174 nigel 75 memory that is obtained via <b>pcre_malloc</b>. The address of the memory block
2175 nigel 63 is returned via <i>listptr</i>, which is also the start of the list of string
2176     pointers. The end of the list is marked by a NULL pointer. The yield of the
2177 nigel 93 function is zero if all went well, or the error code
2178 nigel 63 <pre>
2180 nigel 75 </pre>
2181 nigel 63 if the attempt to get the memory block failed.
2182     </P>
2183     <P>
2184     When any of these functions encounter a substring that is unset, which can
2185     happen when capturing subpattern number <i>n+1</i> matches some part of the
2186     subject, but subpattern <i>n</i> has not been used at all, they return an empty
2187     string. This can be distinguished from a genuine zero-length substring by
2188     inspecting the appropriate offset in <i>ovector</i>, which is negative for unset
2189     substrings.
2190     </P>
2191     <P>
2192     The two convenience functions <b>pcre_free_substring()</b> and
2193     <b>pcre_free_substring_list()</b> can be used to free the memory returned by
2194     a previous call of <b>pcre_get_substring()</b> or
2195     <b>pcre_get_substring_list()</b>, respectively. They do nothing more than call
2196     the function pointed to by <b>pcre_free</b>, which of course could be called
2197     directly from a C program. However, PCRE is used in some situations where it is
2198 nigel 91 linked via a special interface to another programming language that cannot use
2199 nigel 63 <b>pcre_free</b> directly; it is for these cases that the functions are
2200     provided.
2201     </P>
2202 ph10 691 <br><a name="SEC18" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a><br>
2203 nigel 63 <P>
2204 nigel 75 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
2205     <b>const char *<i>name</i>);</b>
2206     </P>
2207     <P>
2208 nigel 63 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
2209     <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
2210     <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
2211     <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
2212     </P>
2213     <P>
2214     <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
2215     <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
2216     <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
2217     <b>const char **<i>stringptr</i>);</b>
2218     </P>
2219     <P>
2220 nigel 75 To extract a substring by name, you first have to find associated number.
2221     For example, for this pattern
2222 nigel 63 <pre>
2223 nigel 93 (a+)b(?&#60;xxx&#62;\d+)...
2224 nigel 75 </pre>
2225 nigel 91 the number of the subpattern called "xxx" is 2. If the name is known to be
2226     unique (PCRE_DUPNAMES was not set), you can find the number from the name by
2227     calling <b>pcre_get_stringnumber()</b>. The first argument is the compiled
2228     pattern, and the second is the name. The yield of the function is the
2229 nigel 75 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
2230     that name.
2231 nigel 63 </P>
2232     <P>
2233 nigel 75 Given the number, you can extract the substring directly, or use one of the
2234     functions described in the previous section. For convenience, there are also
2235     two functions that do the whole job.
2236 nigel 63 </P>
2237     <P>
2238 nigel 91 Most of the arguments of <b>pcre_copy_named_substring()</b> and
2239     <b>pcre_get_named_substring()</b> are the same as those for the similarly named
2240 nigel 75 functions that extract by number. As these are described in the previous
2241     section, they are not re-described here. There are just two differences:
2242 nigel 63 </P>
2243     <P>
2244     First, instead of a substring number, a substring name is given. Second, there
2245     is an extra argument, given at the start, which is a pointer to the compiled
2246     pattern. This is needed in order to gain access to the name-to-number
2247     translation table.
2248     </P>
2249     <P>
2250     These functions call <b>pcre_get_stringnumber()</b>, and if it succeeds, they
2251 ph10 128 then call <b>pcre_copy_substring()</b> or <b>pcre_get_substring()</b>, as
2252     appropriate. <b>NOTE:</b> If PCRE_DUPNAMES is set and there are duplicate names,
2253     the behaviour may not be what you want (see the next section).
2254 nigel 63 </P>
2255 ph10 392 <P>
2256 ph10 461 <b>Warning:</b> If the pattern uses the (?| feature to set up multiple
2257     subpatterns with the same number, as described in the
2258     <a href="pcrepattern.html#dupsubpatternnumber">section on duplicate subpattern numbers</a>
2259     in the
2260     <a href="pcrepattern.html"><b>pcrepattern</b></a>
2261     page, you cannot use names to distinguish the different subpatterns, because
2262     names are not included in the compiled code. The matching process uses only
2263     numbers. For this reason, the use of different names for subpatterns of the
2264     same number causes an error at compile time.
2265 ph10 392 </P>
2266 ph10 691 <br><a name="SEC19" href="#TOC1">DUPLICATE SUBPATTERN NAMES</a><br>
2267 nigel 63 <P>
2268 nigel 91 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
2269     <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
2270     </P>
2271     <P>
2272     When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
2273 ph10 461 are not required to be unique. (Duplicate names are always allowed for
2274     subpatterns with the same number, created by using the (?| feature. Indeed, if
2275     such subpatterns are named, they are required to use the same names.)
2276     </P>
2277     <P>
2278     Normally, patterns with duplicate names are such that in any one match, only
2279     one of the named subpatterns participates. An example is shown in the
2280 nigel 91 <a href="pcrepattern.html"><b>pcrepattern</b></a>
2281 ph10 208 documentation.
2282     </P>
2283     <P>
2284     When duplicates are present, <b>pcre_copy_named_substring()</b> and
2285     <b>pcre_get_named_substring()</b> return the first substring corresponding to
2286     the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING (-7) is
2287     returned; no data is returned. The <b>pcre_get_stringnumber()</b> function
2288     returns one of the numbers that are associated with the name, but it is not
2289     defined which it is.
2290     </P>
2291     <P>
2292 nigel 91 If you want to get full details of all captured substrings for a given name,
2293     you must use the <b>pcre_get_stringtable_entries()</b> function. The first
2294     argument is the compiled pattern, and the second is the name. The third and
2295     fourth are pointers to variables which are updated by the function. After it
2296     has run, they point to the first and last entries in the name-to-number table
2297     for the given name. The function itself returns the length of each entry, or
2298 nigel 93 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
2299 ph10 654 described above in the section entitled <i>Information about a pattern</i>
2300     <a href="#infoaboutpattern">above.</a>
2301 nigel 93 Given all the relevant entries for the name, you can extract each of their
2302     numbers, and hence the captured data, if any.
2303 nigel 91 </P>
2304 ph10 691 <br><a name="SEC20" href="#TOC1">FINDING ALL POSSIBLE MATCHES</a><br>
2305 nigel 91 <P>
2306 nigel 77 The traditional matching function uses a similar algorithm to Perl, which stops
2307     when it finds the first match, starting at a given point in the subject. If you
2308     want to find all possible matches, or the longest possible match, consider
2309     using the alternative matching function (see below) instead. If you cannot use
2310     the alternative function, but still need to find all possible matches, you
2311     can kludge it up by making use of the callout facility, which is described in
2312     the
2313     <a href="pcrecallout.html"><b>pcrecallout</b></a>
2314     documentation.
2315     </P>
2316     <P>
2317     What you have to do is to insert a callout right at the end of the pattern.
2318     When your callout function is called, extract and save the current matched
2319     substring. Then return 1, which forces <b>pcre_exec()</b> to backtrack and try
2320     other alternatives. Ultimately, when it runs out of matches, <b>pcre_exec()</b>
2321     will yield PCRE_ERROR_NOMATCH.
2322     <a name="dfamatch"></a></P>
2323 ph10 691 <br><a name="SEC21" href="#TOC1">MATCHING A PATTERN: THE ALTERNATIVE FUNCTION</a><br>
2324 nigel 77 <P>
2325     <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
2326     <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
2327     <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
2328     <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
2329     </P>
2330     <P>
2331     The function <b>pcre_dfa_exec()</b> is called to match a subject string against
2332 nigel 93 a compiled pattern, using a matching algorithm that scans the subject string
2333     just once, and does not backtrack. This has different characteristics to the
2334     normal algorithm, and is not compatible with Perl. Some of the features of PCRE
2335     patterns are not supported. Nevertheless, there are times when this kind of
2336 ph10 461 matching can be useful. For a discussion of the two matching algorithms, and a
2337 ph10 453 list of features that <b>pcre_dfa_exec()</b> does not support, see the
2338 nigel 77 <a href="pcrematching.html"><b>pcrematching</b></a>
2339     documentation.
2340     </P>
2341     <P>
2342     The arguments for the <b>pcre_dfa_exec()</b> function are the same as for
2343     <b>pcre_exec()</b>, plus two extras. The <i>ovector</i> argument is used in a
2344     different way, and this is described below. The other common arguments are used
2345     in the same way as for <b>pcre_exec()</b>, so their description is not repeated
2346     here.
2347     </P>
2348     <P>
2349     The two additional arguments provide workspace for the function. The workspace
2350     vector should contain at least 20 elements. It is used for keeping track of
2351     multiple paths through the pattern tree. More workspace will be needed for
2352 nigel 91 patterns and subjects where there are a lot of potential matches.
2353 nigel 77 </P>
2354     <P>
2355 nigel 87 Here is an example of a simple call to <b>pcre_dfa_exec()</b>:
2356 nigel 77 <pre>
2357     int rc;
2358     int ovector[10];
2359     int wspace[20];
2360 nigel 87 rc = pcre_dfa_exec(
2361 nigel 77 re, /* result of pcre_compile() */
2362     NULL, /* we didn't study the pattern */
2363     "some string", /* the subject string */
2364     11, /* the length of the subject string */
2365     0, /* start at offset 0 in the subject */
2366     0, /* default options */
2367     ovector, /* vector of integers for substring information */
2368     10, /* number of elements (NOT size in bytes) */
2369     wspace, /* working space vector */
2370     20); /* number of elements (NOT size in bytes) */
2371     </PRE>
2372     </P>
2373     <br><b>
2374     Option bits for <b>pcre_dfa_exec()</b>
2375     </b><br>
2376     <P>
2377     The unused bits of the <i>options</i> argument for <b>pcre_dfa_exec()</b> must be
2378 nigel 91 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
2382     All but the last four of these are exactly the same as for <b>pcre_exec()</b>,
2383     so their description is not repeated here.
2384 nigel 77 <pre>
2385 ph10 429 PCRE_PARTIAL_HARD
2386 ph10 461 PCRE_PARTIAL_SOFT
2387 nigel 77 </pre>
2388 ph10 429 These have the same general effect as they do for <b>pcre_exec()</b>, but the
2389     details are slightly different. When PCRE_PARTIAL_HARD is set for
2390     <b>pcre_dfa_exec()</b>, it returns PCRE_ERROR_PARTIAL if the end of the subject
2391     is reached and there is still at least one matching possibility that requires
2392     additional characters. This happens even if some complete matches have also
2393     been found. When PCRE_PARTIAL_SOFT is set, the return code PCRE_ERROR_NOMATCH
2394     is converted into PCRE_ERROR_PARTIAL if the end of the subject is reached,
2395     there have been no complete matches, but there is still at least one matching
2396 ph10 453 possibility. The portion of the string that was inspected when the longest
2397     partial match was found is set as the first matching string in both cases.
2398 ph10 567 There is a more detailed discussion of partial and multi-segment matching, with
2399     examples, in the
2400     <a href="pcrepartial.html"><b>pcrepartial</b></a>
2401     documentation.
2402 nigel 77 <pre>
2404     </pre>
2405     Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
2406 nigel 93 soon as it has found one match. Because of the way the alternative algorithm
2407     works, this is necessarily the shortest possible match at the first possible
2408     matching point in the subject string.
2409 nigel 77 <pre>
2411     </pre>
2412 ph10 429 When <b>pcre_dfa_exec()</b> returns a partial match, it is possible to call it
2413     again, with additional subject characters, and have it continue with the same
2414     match. The PCRE_DFA_RESTART option requests this action; when it is set, the
2415     <i>workspace</i> and <i>wscount</i> options must reference the same vector as
2416     before because data about the match so far is left in them after a partial
2417     match. There is more discussion of this facility in the
2418 nigel 77 <a href="pcrepartial.html"><b>pcrepartial</b></a>
2419     documentation.
2420     </P>
2421     <br><b>
2422     Successful returns from <b>pcre_dfa_exec()</b>
2423     </b><br>
2424     <P>
2425     When <b>pcre_dfa_exec()</b> succeeds, it may have matched more than one
2426     substring in the subject. Note, however, that all the matches from one run of
2427     the function start at the same point in the subject. The shorter matches are
2428     all initial substrings of the longer matches. For example, if the pattern
2429     <pre>
2430     &#60;.*&#62;
2431     </pre>
2432     is matched against the string
2433     <pre>
2434     This is &#60;something&#62; &#60;something else&#62; &#60;something further&#62; no more
2435     </pre>
2436     the three matched strings are
2437     <pre>
2438     &#60;something&#62;
2439     &#60;something&#62; &#60;something else&#62;
2440     &#60;something&#62; &#60;something else&#62; &#60;something further&#62;
2441     </pre>
2442     On success, the yield of the function is a number greater than zero, which is
2443     the number of matched substrings. The substrings themselves are returned in
2444     <i>ovector</i>. Each string uses two elements; the first is the offset to the
2445 nigel 93 start, and the second is the offset to the end. In fact, all the strings have
2446     the same start offset. (Space could have been saved by giving this only once,
2447     but it was decided to retain some compatibility with the way <b>pcre_exec()</b>
2448     returns data, even though the meaning of the strings is different.)
2449 nigel 77 </P>
2450     <P>
2451     The strings are returned in reverse order of length; that is, the longest
2452     matching string is given first. If there were too many matches to fit into
2453     <i>ovector</i>, the yield of the function is zero, and the vector is filled with
2454 ph10 691 the longest matches. Unlike <b>pcre_exec()</b>, <b>pcre_dfa_exec()</b> can use
2455     the entire <i>ovector</i> for returning matched strings.
2456 nigel 77 </P>
2457     <br><b>
2458     Error returns from <b>pcre_dfa_exec()</b>
2459     </b><br>
2460     <P>
2461     The <b>pcre_dfa_exec()</b> function returns a negative number when it fails.
2462     Many of the errors are the same as for <b>pcre_exec()</b>, and these are
2463     described
2464     <a href="#errorlist">above.</a>
2465     There are in addition the following errors that are specific to
2466     <b>pcre_dfa_exec()</b>:
2467     <pre>
2468     PCRE_ERROR_DFA_UITEM (-16)
2469     </pre>
2470     This return is given if <b>pcre_dfa_exec()</b> encounters an item in the pattern
2471     that it does not support, for instance, the use of \C or a back reference.
2472     <pre>
2473     PCRE_ERROR_DFA_UCOND (-17)
2474     </pre>
2475 nigel 93 This return is given if <b>pcre_dfa_exec()</b> encounters a condition item that
2476     uses a back reference for the condition, or a test for recursion in a specific
2477     group. These are not supported.
2478 nigel 77 <pre>
2480     </pre>
2481     This return is given if <b>pcre_dfa_exec()</b> is called with an <i>extra</i>
2482 ph10 691 block that contains a setting of the <i>match_limit</i> or
2483     <i>match_limit_recursion</i> fields. This is not supported (these fields are
2484     meaningless for DFA matching).
2485 nigel 77 <pre>
2486     PCRE_ERROR_DFA_WSSIZE (-19)
2487     </pre>
2488     This return is given if <b>pcre_dfa_exec()</b> runs out of space in the
2489     <i>workspace</i> vector.
2490     <pre>
2492     </pre>
2493     When a recursive subpattern is processed, the matching function calls itself
2494     recursively, using private vectors for <i>ovector</i> and <i>workspace</i>. This
2495     error is given if the output vector is not large enough. This should be
2496     extremely rare, as a vector of size 1000 is used.
2497     </P>
2498 ph10 691 <br><a name="SEC22" href="#TOC1">SEE ALSO</a><br>
2499 nigel 77 <P>
2500 nigel 93 <b>pcrebuild</b>(3), <b>pcrecallout</b>(3), <b>pcrecpp(3)</b>(3),
2501     <b>pcrematching</b>(3), <b>pcrepartial</b>(3), <b>pcreposix</b>(3),
2502     <b>pcreprecompile</b>(3), <b>pcresample</b>(3), <b>pcrestack</b>(3).
2503     </P>
2504 ph10 691 <br><a name="SEC23" href="#TOC1">AUTHOR</a><br>
2505 nigel 93 <P>
2506 ph10 99 Philip Hazel
2507 nigel 63 <br>
2508 ph10 99 University Computing Service
2509     <br>
2510     Cambridge CB2 3QH, England.
2511     <br>
2512     </P>
2513 ph10 691 <br><a name="SEC24" href="#TOC1">REVISION</a><br>
2514 ph10 99 <P>
2515 ph10 784 Last updated: 02 December 2011
2516 ph10 99 <br>
2517 ph10 654 Copyright &copy; 1997-2011 University of Cambridge.
2518 ph10 99 <br>
2519 nigel 75 <p>
2520     Return to the <a href="index.html">PCRE index page</a>.
2521     </p>


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